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Integrated energy systems (IESs) are an emerging approach to maximize efficiency and resilience for residential and commercial air conditioning and water heating loads using gas-fired, electrically-driven and/or renewable off-the-self components with distributed energy resources (DER) and energy storage. IESs include a myriad of equipment combinations, such as furnaces, water heaters and air-source heat pumps (ASHPs), on-site power from micro combined heat and power (mCHP) and solar photovoltaics (PV), as well as electrical and thermal energy storage. When properly integrated and controlled, IESs can serve to balance energy grid supply and demand while exploiting multiple energy sources in ways that improve overall operating cost and efficiencies, minimize emission levels, and provide resilient systems in the built environment. This paper describes an IES developed for residential cold-climate low-load homes driven by customized controls developed by GTI Energy to manage thermal and power generation and storage of a mCHP in a nano-grid environment for space and water heating loads. The IES included an ASHP, hydronic air handler unit (AHU), buffer tank and gas-fired tankless water heater (TWH) powered by mCHP and PV reducing grid power demand. GTI Energy used its Virtual Test Home (VTH) test platform, which applies simulated-use loads to the IES in a dynamic interaction between building energy models and test rigs. The IES was evaluated with real-time weather and corresponding simulated loads using different nano-grid configurations during the heating and cooling seasons. The nano-grids were developed such that power and thermal outputs from the mCHP reduced operating cost and GHGs relative to traditional HVAC solutions. Daily performance results for the IES from the VTH evaluations are presented to demonstrate the pros and cons of each nanogrid configuration. This paper includes a modeled comparison of the IES operating cost and emissions levels relative to commercially available advanced all-electric and fuel-fired systems for residential space and water heating applications. [ABSTRACT FROM AUTHOR]

Heat pump water heaters (HPWHs) offer an efficient way to heat water using electricity, which aligns with efforts toward decarbonization and better utilization of renewable energy sources. Economic model predictive control (EMPC) provides an automated way to provide load flexibility of this new electric load by accounting for exogenous inputs like time-varying electric rates or marginal greenhouse gas emissions. Furthermore, a cloud-based supervisory controller implementation of EMPC enables retrofitting existing HPWHs with cloud-connection. In this work, the formulation of a supervisory multiobjective EMPC for HPWH is presented. The formulation of a supervisory multi-objective EMPC for HPWH is presented for equipment with a single heat pump and up to two backup resistive heating elements. A temperature setpoint is computed from the EMPC decisions using a logic-based setpoint calculator so the existing HPWH rule-based control (RBC) strategy activates the desired heat sources when deemed optimal by the EMPC. The performance of the simulated testing results under the supervisory EMPC is compared against the performance under an RBC strategy and under a regulatory EMPC that directly controls the HPWH. The simulation results demonstrate that the RBC in the proposed control architecture, operates the HPWH heat sources in the optimal manner computed by the EMPC, which indicates that the setpoint calculator can translate EMPC decisions to appropriate temperature setpoints. To minimize heat pump cycling, the effect of increasing the minimum on-time for the heat pump is also considered and the results show that increasing the minimum on-time increases the operating cost. [ABSTRACT FROM AUTHOR]

Micro combined heat and power (mCHP) is an emerging technology that can simultaneously produce onsite heat and power for residential, light commercial and industrial applications. These systems operate in parallel with the grid or islanded from the grid and in conjunction with other equipment to supplement or meet building power and thermal loads. mCHP systems can be integrated with other appliances to minimize operational costs by improving the overall system efficiencies as well as reduce greenhouse gas emissions associated with residential space conditioning and water heating. Such integrated energy systems (IESs) include a myriad of equipment combinations in addition to the mCHP, such as renewable power sources, thermal and electric energy storage, as well as traditional equipment such as furnaces, water heaters and heat pumps. IESs can be implemented in nanogrid configurations that allow for self-sustained HVAC and water heating independent of grid power. However, many nano-grid systems are designed around autonomous backup generators that do not operate in parallel with other power sources such as the grid. These systems often integrate the backup generators with renewable photovoltaics and battery storage that can be oversized due to intermittency and short-term operation of backup generators. This paper will discuss challenges and solutions associated with grid-tied and off-grid mCHP applications that use various nano-grid controllers to integrate mCHP systems with other bi-directional power sources, hybrid electric and fuel-fired HVAC and water heating systems, electric vehicle charging, and thermal and electric energy storage in Residential homes. The paper identifies potential benefits of interactive nanogrid or microgrid features that manage power and thermal sources and loads in real time to maximize efficiencies, minimize greenhouse gases and minimize operating costs. [ABSTRACT FROM AUTHOR]

In this paper, the authors summarize data and key findings from the demonstration of thermally driven heat pump (TDHP) combination space heating (SH) and domestic hot water (DHW) systems. TDHP systems are innovative fuel-fired heat pumps installed in "combi" applications for residential and commercial SH and DHW solutions. The TDHP can be retrofitted for both (a) SH in place of a traditional furnace, and (b) DHW in place of a conventional water heater. Major components of the system are the TDHP, providing high-efficiency heating via a single-effect ammonia absorption cycle, an indirect storage tank (IST), and an indoor hydronic air handler unit (AHU), which is installed in place of a furnace. According to the US EIA, of the estimated total natural gas consumed by the United States in 2020, 15% or 4.65 trillion therms (.465 Exajoules) were consumed by the residential sector (U.S. EIA). While this encompasses all residential gas use, a majority of this is space and DHW heating. Most residential SH and DHW systems utilize low-efficiency furnaces and water heaters with thermal efficiencies of ~80% and ~62%, respectively. With an estimated improvement of operating efficiency up to ~140% for the combi operational mode, broad deployment of TDHP combis could reduce natural gas consumption by up to 53% compared to the typical gas heating case, with commensurate reduction in CO2-equivalent emissions. The crucial factor in achieving a higher delivered efficiency from the TDHP is the optimization of its controls, minimizing losses, and right-sizing. When optimized for performance, the TDHP can operate in a quasi-steady state mode with reduced part-load losses, as verified by lab test data. If these conditions are not met because cycles are too short or varied, if the TDHP is consistently load-following, or the controls are improperly responding to SH or DHW calls, then system delivered efficiencies will suffer. Additionally, installation best practices such as fully insulated hydronic lines, short hydronic loop lengths, proper hydronic glycol percentage, and more must be followed so that heating losses are minimized. The relationship between each of these and system efficiencies was assessed via lab testing of TDHP combis and in field demonstrations across sites located in Illinois, Wisconsin, and Ontario. By analyzing system performances over a wider sample size, under a variety of operating conditions and loads, the importance of system design and optimization can be better understood to aid in the future implementation of heat pump combi systems and can be a pathway for greenhouse gas reductions. [ABSTRACT FROM AUTHOR]

Decarbonization of the buildings sector utilizing hydrogen has become a promising technical option to combat global warming. Therefore, blending hydrogen into natural gas infrastructures and providing low carbon fuels to appliances is being investigated worldwide. To facilitate the upcoming energy transition in building gas transmission, testing of existing appliances performance while operating on natural gas/hydrogen mixtures need to be conducted. In this study, various methane/hydrogen blends were supplied to a tankless water heater to study on the hydrogen impact on the water heater performances. The hydrogen percentage in the fuel mixture varied from 0% up to 30 vol%. In hydrogen blending efforts, it is of great interest for both gas utility companies and facility operators to be aware of the exact hydrogen percentage in the pipeline before or during combustion device operation. Moreover, there are also questions regarding hydrogen stratification and segregation after blending, due to the low density of hydrogen compared to the heavier hydrocarbons in natural gas infrastructures. Therefore, under this project, two inline gas sensors were installed in the residential pipeline to monitor the hydrogen contents and other fuel properties in real time, synchronized with the tankless water heater testing. This project demonstrates the feasibility for existing natural gas appliances operating on hydrogen-enriched fuels, with the gas contents being monitored using inexpensive sensors. This study provides the near future scope of gas utilities or gas consumers monitoring the gas contents in the pipeline with gas flowing into end use devices. The demonstrated example, using a varied-heating load tankless water heater with the highest gas input rate of 199,000 Btu/hr (58 kw) operating on natural gas/hydrogen blends, demonstrates the potential for domestic appliances carbon reduction using hydrogen. [ABSTRACT FROM AUTHOR]

Power-to-Gas is gaining interest in the energy industry to support broad decarbonization goals by storing excess renewable electricity as hydrogen in the existing gas grid, which can then be consumed in blends with natural gas by existing combustion systems. Hydrogen offers a significant means of seasonal energy storage at energy densities not matched by electric batteries and could create additional value for renewable electricity projects, which may otherwise curtail generation during periods of excess capacity. While multiple pilots are already underway in Europe and North America, these studies are in their infancy. More work is still needed to develop the underlying technologies and to demonstrate safety, reliability, and economic benefits of the approach. Multiple studies have identified that end use appliances (residential, commercial, and industrial combustion systems) are likely to pose the lowest limits of hydrogen compatibility when no changes are made to the burners and controls. Limits of compatibility of 15% to 30% of hydrogen by volume have been cited. The wide range of blending limits is in large part due to the variety of gas combustion systems used throughout the world. In North American residential and commercial applications, the vast majority of the natural gas burners are low-cost, atmospheric partial premix burners, found in appliances such as gas furnaces, boilers, water heaters, as well as non-HVAC equipment such as cooking ranges and gas dryers. Partial premix burners are characterized by low-pressure injection of fuel into the burner which entrains 50-70% of the total air required for combustion, with the balance made up as secondary air at the flame. These types of burners have been extensively used since the 19th century for their stability, efficiency, and high turn-down. For this reason, the design approaches used in the product development of partial premix gas-fired appliances have not substantially changed since the mid-20th Century when a broad transition from the use of town gas (up to 50% hydrogen) to natural gas occurred. This paper summarizes the results of a theoretical investigation into fundamentals of gas burner designs, identifying important characteristics that may permit or restrict their compatibility with hydrogen-blended gas, as well as the interrelated effects of hydrogen blending on burners designed for natural gas. [ABSTRACT FROM AUTHOR]

Load shifting entails moving home electricity use from on-peak hours to off-peak hours, thus resulting in reduced utility bills. Given the Time of Use (TOU) rate, the load shifting can be achieved by scheduling the smart home appliances in advance. However, the operations of the home appliances interfere with each other. For example, the heat dissipation of some appliances might contribute to the cooling load for the HVAC system. In contrast, a lower indoor air temperature might affect the heat loss rate of other appliances. In this study, we developed a connected home energy management system including different types of appliances. 2R2C thermal model was used to predict the behavior of the HVAC system, whose operation is controlled thermostatically. Similarly, a first-order differential equation was used for the water heater system. To achieve more effective control, we adopted a learning-based system identification framework for the 2R2C model and characterized three major coupling effects between different appliances. Peak load management is also considered in the model to avoid possible financial penalties caused by the high demand in a short amount of time. A case study was carried out by scheduling the operations of the appliances 24 hours ahead in a single-story test house located in Norman, Oklahoma. The results with data obtained from a smart thermostat indicated that the 2R2C model was accurate with a mean absolute error as low as 0.559 F. The 24-hour scheduling results indicated that most appliances tried to avoid the on-peak hours, the HVAC system chose to precool the air, and the water heater chose to preheat the water. The proposed energy management system can be easily adapted into the IoT-based home automation system. [ABSTRACT FROM AUTHOR]

Future utilities will emphasize home appliances to reduce greenhouse gas emissions while providing electric load shifting and demand profile management. Heat pump water heaters (HPWH) have demonstrated the ability to cut water heating energy by more than 65% compared with conventional electric resistance waters (ERWH). Laboratory research was conducted on the load shifting potential of grid-connected heat pump water heaters (HPWH), compared to ERWHs. Testing applied different CTA-2045 command designs. Highly-controlled laboratory experiments were conducted on one ERWH and four HPWHs, including a prototype incorporating the new CTA-2045-B protocol feature allowing 'advanced' load up above the tank setpoint. The prototype unit with the B-protocol increased tank temperature by 15oF (8.3C) under the advanced load up providing an increase of 1.8 kWh of storage for a 50-gallon (189 liter) tank. The prototype includes a built-in mixing valve to meet anti-scalding codes. With the load-shaping ability of CTA-2045-B, utilities might be able to store excess renewable energy in connected tanks when renewable wind and solar resource production is high. Tests were performed under baseline conditions (no load shift) and under several load-shifting schemes, including load up and advanced load up, ahead of shed commands. Gridconnected HPWHs reduced peak demand by as much as 0.5 kW, depending on tank volume, time of day, control scheme, and draw profile. [ABSTRACT FROM AUTHOR]

The Kingdoms’ electricity consumption has been steadily increasing during the past 10 years, with the residential sector consuming nearly 45% of it. Therefore, the residential sector offers a real opportunity for energy savings, as one of the reasons for this high-energy consumption is the utilization of low efficiency electric home appliances, e.g., electric water heaters (EWH). This behavior is encouraged due to the low initial investment for inefficient appliances, compared to the more efficient ones. Electric Heat Pump Water Heater (EHPWH) can substantially reduce water-heating-related energy use in the Saudi residential sector. This paper investigates the potential savings in primary energy, and its corresponding carbon dioxide (CO2) reduction, achieved by switching from conventional low efficiency electric resistance water heaters to EHPWH. The potential energy savings is nearly 0.19 Quadrillion Btu (0.20 Exajoules), and a corresponding 28,660 million pounds (13 million metric tons) of CO2 emissions reduction. This study paves the road for policy makers to take a deep dive investigation of this proposal. [ABSTRACT FROM AUTHOR]

Both cold-climate air-source heat pumps (ccASHPs) and heat pump water heaters (EHPWHs) have gained significant popularity due to increasing interest towards electrification of residential HVAC and water heating appliances. Seasonal Energy Efficiency Ratio (SEER), Heating Seasonal Performance Factor (HSPF) and Uniform Energy Factor (UEF) ratings used by manufacturers to compare appliance efficiencies cannot determine the efficiency of a HVAC and water heating system in multiple climate zones or integrate impact associated to the appliances interaction. This paper describes the resulting performance characterizations of a ccASHP and an EHPWH from an alternative evaluation method developed by GTI to compare residential appliances as installed, the Virtual Test Home (VTH). SEER, HSPF and UEF ratings are not useful for HVAC engineers when selecting equipment for the most efficient HVAC and water heating system based on climate zone or understanding the interaction amongst appliances. The VTH identifies the parameters that affect individual space heating/cooling and water heating appliances performance throughout a series of laboratory evaluations. Performance curves and modeling algorithms are developed for each appliance and implemented in building energy models to estimate a HVAC and water heating system annual energy consumption, operating costs and GHG emissions. This paper presents the estimated combined ccASHP and EHPWH annual efficiencies, operating costs and GHG emissions in a lowload home in multiple International Energy Conservation Code (IECC) climate zones. VTH evaluations are suitable for the energy community to compare residential HVAC and water heating systems in terms of annual energy and cost savings and greenhouse gas (GHG) emission reductions in multiple climates and grid zones amongst other operating conditions. This metric can potentially allow HVAC engineers to make informative decisions when selecting appliances for HVAC and water heating systems considering as installed annual operating costs and GHG emissions. Additionally, manufacturers can implement such evaluation methods to optimize individual appliance performance considering multiple climate zones. [ABSTRACT FROM AUTHOR]

Water heating is a major energy consumption in the US residential sector. According to the annual energy outlook of the EIA (EIA 2021), the total US national primary energy efficiency of water heating is only 60%. Heat pump water heaters can significantly increase the thermal efficiency of water heating. Electric powered heat pump water heaters are already commercially available in the US. On the other hand, no fuel-fired heat pump water heaters are available, but two are in development, both employ absorption cycle. Thermally driven ejector heat pumps have been discounted for their low efficiency and narrow operating range. In this paper we present performance analysis of a novel ejector heat pump for water heating that overcomes the shortcomings of conventional ejector heat pumps. The heat pump uses binary fluid mixture and active back pressure control. The use of the binary mixture results in high thermal efficiency and the active back pressure control widens the operating range of the heat pump. Two configurations of the heat pump are presented and analyzed. The maximum achievable COP of each was 1.95 and 1.7 at output heating capacities of 5.7 and 6.7 kW, respectively. [ABSTRACT FROM AUTHOR]

Integrated Energy Systems (IES) are an emerging approach to self-powered HVAC and water heating that integrate fuel-fired and electrically powered equipment with Distributed Energy Resources (DER) and energy storage. In this paper, the authors describe hybrid and grid-interactive IES designs and approaches that serve to balance energy grid supply and demand while exploiting multiple energy resources in ways that improve overall operating cost and efficiencies, minimize emission levels, and provide resilient systems in the built environment. IES includes a myriad of equipment combinations including traditional furnaces, water heaters and heat pumps, on-site power from small-scale combined heat and power and photovoltaics, as well as electrical and thermal energy storage. Individually, these systems have key attributes including high efficiency, low cost of operation, delivered comfort, and energy resilience. However, operated in isolation, the equipment can only provide those attributes some of the time. A comprehensive approach including laboratory, modeling, and field research indicates proper configuration and control of these systems, and when grid connected, can demonstrate far better performance integrated and connected than when isolated. In addition to gaining an in depth understanding of individual equipment performances through extensive simulated use testing, the authors examine different approaches to integrating various off-the-shelf equipment components by simulating the complex interaction of multiple energy systems within single buildings as well as the greater grid. Findings indicate specific IES designs can achieve self-powered space heating/cooling and water heating at annual coefficients of performance greater than 1.0 on a source energy basis with 30% to 50% less operating costs and similar greenhouse gas emissions savings than with separate code compliant equipment in various climates. [ABSTRACT FROM AUTHOR]

The performance of solar-assisted water heaters is limited by the absorption properties of the working fluid and it can be improved by replacing them with highly conductive nanofluids. However, the idea of using nanofluids have not been completely commercialized and many works are only being focused on the steady-state analysis of Solar Assisted Water Heaters (SAWH) which don't reflect a practical scenario. Hence, this works aims at analyzing the performance of a SAWH installed in a multi-residential building in Greece Climatic Conditions using TRNSYS and MATLAB with aluminium oxide nanofluid as the working fluid. It was found that upon including 0.1% volume concentration and 13 nm (4.2651 × 10-8 foot) particle-sized aluminium oxide nanofluid, the annual energy consumption dropped from 330 kWh (1.1 × 106 Btu) to 279 kWh (9.5 × 105 Btu). Further, the maximum energy and exergy efficiency increased to around 52% and 2.5% respectively. Upon performing the exergy analysis, it was found that the contribution of exergy destruction between the plate and the fluid is only about 20% of the total exergy destruction. Though this percentage is small, this works aims at reducing this component of exergy destruction for further enhancement of the system. It can be finally concluded that adding nanofluids to the system is a prudent option of increasing the performance. However, around 80% of the total exergy destruction occurs in the flat plate collector. Hence, a novel change in the design of the collector is essential to reduce this part of exergy destruction and to improve the system's performance. [ABSTRACT FROM AUTHOR]

In this paper the authors summarize data and key findings from the demonstration of integrated thermal heat pump (THP) systems, which are innovative "hybrid" commercial water heating solutions installed such that the THP provides (a) hot water in series with conventional water heater(s), and (b) A/C supplemental to the building HVAC. Major components are the THP, providing high-efficiency heating and 'free cooling' to separate hydronic/chilled water loops, an indirect storage tank in series with conventional water heater (s), and an indoor cooling coil installed as standalone or within the ductwork. At its core is the THP, a direct-fired absorption heat pump providing hot water and A/C through a four-pipe design, with additional flexibility to operate as an air-source THP during periods of low or no A/C demand. Of the estimated 340 million therms per year consumed for commercial hot water in California restaurants, most are consumed by low-efficiency water heaters with a thermal efficiency of ~80%. With an estimated improvement of operating efficiency to 140% or greater for hot water production, broad deployment of THPs could reduce natural gas consumption for commercial water heating in restaurants by 43%, while displacing up to 20% of electricity demand for A/C, providing further energy and operating cost reductions. This potential is assessed in a year-long demonstration of prototype integrated THP systems at two restaurants in Los Angeles, CA, summarizing system design and optimization, energy savings over a broad range of operating conditions, retrofit installation barriers, and interactive effects with other building systems. [ABSTRACT FROM AUTHOR]

Combined space and water heating systems (combis) use a single gas-fired appliance to cover both the domestic hot water as well as space heating demand in residential applications. While this technology has existed in different forms for decades, only recently has interest in the approach begun to grow again. Emergence of high efficiency, i.e., "tight", homes and the availability of high capacity tankless water heaters, make combi systems based on the latter potentially very effective at reducing the overall consumption of fossil fuels in such dwellings. Over the past ten years, extensive data on the performance of combi systems, both in the field and in the lab has been collected. This work focused on utilizing performance data and simple thermodynamic models for tankless combis to predict their energy use with tools like EnergyPlus. Current capabilities and limitations are discussed, as well as possible sources of uncertainty. [ABSTRACT FROM AUTHOR]

In this paper, detailed experimental evaluation of the performance of a large diameter, shallow bore Ground Heat Exchangers (GHE) is presented. Four GHEs were installed at the test site located in Davis, CA USA. The core of the GHEs were back filled with fine sand. Since soil thermal properties vary with moisture, soil temperatures and moisture at various locations in the ground were recorded along with heat carrier fluid inlet and outlet temperatures and mass flow rates for individual GHE. The central GHE was installed with temperature and moisture sensors in the core (midway between helical and straight pipe), at the borewall, and at 1.11 m (43.7 in., r/rbore= 3.64) and 1.94 m (76.3 in., r/rbore= 6.36) radially from the center of the GHE. Temperature was measured at five depths while moisture was measured at three depths at these locations. An external gas water heater was used to simulate the load from a heat pump by providing hot water at the required temperature. In addition to the single GHE, tests were also carried out involving three GHEs in a straight-line configuration. For cases presented, test durations were varied from continous tests (for 21 hours), to intermittent (4 hours ON and 4 hours OFF). Soil properties (thermal conductivity and specific heat capacity) were measured from soil samples extracted from the site. The experiments were used to validate a Capacitance-resistance numerical model of helical GHEs. [ABSTRACT FROM AUTHOR]

In the U.S., 62% of all housing units in the 50 largest metropolitan areas are served by gas-fired water heaters (67% if Florida is excluded), and for the ~4 million gas-fired storage water heaters sold each year to serve these homes only 5% sold are at or above the EnergyStar ® level of 0.67 Uniform Energy Factor (UEF). This is even more pronounced in California where natural gas fuels water heating in approximately 75% of homes, an installed base of 9 million units, one in four gas-fired water heaters in the U.S., and 95% of homes are served by minimum allowable efficiency products of 0.62 UEF. The availability of higher efficiency options is not the issue, with products available up to 0.88 UEF for storage products and 0.97 UEF for tankless products. Instead, this reflects a historic challenge to broadly deploy high-efficiency water heating products, where the combination of lower cost natural gas and higher equipment and installation costs have limited uptake, leaving a large potential for energy efficiency and emissions reductions. To address this potential, the authors describe an integrated gas-fired heat pump water heater (GHPWH) for residential applications, designed for a direct retrofit and to reduce energy consumption and emissions by 50% or greater over conventional baseline. The GHPWH is based on a direct-fired single-effect vapor absorption cycle using the ammonia-water working pair and incorporates internal heat recovery to achieve a projected 1.2-1.3 UEF, depending on usage patterns. While the design and development of this GHPWH is described in prior publications, here the authors provide an overview of results from an expanded demonstration in Southern California, including as-installed efficiencies versus measured baseline, installation and operating challenges, and qualitative input from installers and the host sites. Additionally, the authors report on a simulation study to quantify the impact of the GHPWH on the home's HVAC system when installed in a semi-conditioned or conditioned space. [ABSTRACT FROM AUTHOR]

Flame-assisted Fuel Cells (FFC) have been shown to be uniquely suited for Combined Heat and Power (CHP) applications. In this work, a case study for evaluating the effects of integrating a Flame-assisted Fuel Cell (FFC) stack with a residential water heater is presented. The integrated setup can generate electricity at 21% efficiency at an equivalence ratio of 2.8 with high combined efficiency. The natural gas flow rate and efficiency are analyzed for the case of a fixed thermal output. [ABSTRACT FROM AUTHOR]

Hot-water use in hotels and its associated energy use is significant. However, information on hotel hot-water use patterns has been limited until now, resulting in most hotel hotwater systems being designed using extremely old hot-water use data (45 to 80 years old) that predate the introduction of water and energy-efficient fixtures and appliances. In recognition of this fact, ASHRAE funded Research Project RP-1544 "Establishing Benchmark Levels and Patterns of Commercial Hot-water Use--Hotels" to both develop a monitoring methodology that could be duplicated by others to collect hot-water use data from a larger number of hotels and to obtain updated hot-water use information from at least two hotels. This paper compares hot-water use results collected for a "travel" hotel that had neither meeting rooms nor food service and a "business" hotel that had both. This paper further discusses how to normalize this information so it is useful for sizing hot-water systems for hotels with differing numbers of guest rooms than those tested. A companion paper released simultaneously with this paper describes how to use this information to select water heating systems for hotels of any desired size, and compares results of this sizing method to other hotel hot-water system sizing methods described in ASHRAE Handbook--HVAC Applications, Chapter 50, Service Water Heating, through the use of examples. [ABSTRACT FROM AUTHOR]

Hot-water use in hotels and its associated energy use is significant. However, information on hotel hot-water use patterns has been limited until now, resulting in most hotel hotwater systems being designed using extremely old hot-water use data (45 to 80 years old) that predate the introduction of water and energy-efficient fixtures and appliances. In recognition of this fact, ASHRAE funded Research Project RP-1544 "Establishing Benchmark Levels and Patterns of Commercial Hot-Water Use-Hotels" to both develop a monitoring methodology that could be duplicated by others to collect hot-water use data from a larger number of hotels and to obtain updated hot-water use information from at least two hotels. This paper builds on information presented in the project final report, the three previously published papers, and a fourth paper released simultaneously with thispaperto present informationonusing theupdated data to select water heating systems for hotels of any desired size and compares results of this sizing method to other hotel hotwater system sizing methods described in ASHRAE Handbook--HVAC Applications, Chapter 50, Service Water Heating (ASHRAE 2015) through the use of examples. [ABSTRACT FROM AUTHOR]

An analytical study is carried out to assess the impact of corrections to nominal test conditions on the measured energy factor for residential water heaters. While test conditions are specified in the method of test, the difficulty in exactly achieving these test conditions in the laboratory necessitates a computational approach to correct the results to nominal conditions. This paper examines the magnitude of those corrections for a range of water heaters of various fuel type, heating method, and size across a number of potential draw volumes during a 24-hour simulated use test. In making these corrections, a recovery efficiency and a standby heat loss coefficient are determined during the test; the effects of variations in those measured values on the resultant energy factor are discussed. Finally, the impact of tighter test tolerances on the variability of the energy factor is investigated to assist in evaluating the benefits of changing test conditions. [ABSTRACT FROM AUTHOR]

When operating properly, the combination of a gas-fired condensing boiler with baseboard convectors and an indirect water heater is a viable option for high-efficiency residential space heating in cold climates. Based on previous research efforts, however, it is apparent that these systems are typically not designed and installed to achieve maximum efficiency. Outdoor reset curves, flow rates, baseboard capacity and control options were not optimized in any of the systems monitored. In cooperation with the DOE's Building America program, researchers attempted to determine the optimal combination(s) of components -- pumps, high efficiency heat sources, plumbing configurations and controls -- that result in the highest overall efficiency for a hydronic system where baseboard convectors are used as the heat emitter. Two distinct systems were designed and monitored for a full heating season: 1) a high mass condensing water heater, and 2) a condensing boiler with an indirect tank. The boiler was configured with the option to alternate between a standard primary/secondary loop and a buffer tank to analyze the effects of added mass on short cycling and overall system efficiency. Thermostat setback was found to be the most economical mode of operation, despite the fact that control options that override the outdoor reset control were employed which reduced condensing. Specialized controls for overriding the outdoor reset control were found to drastically reduce response to thermostat setback. Short cycling, inherent in low-load homes, was drastically reduced by controls that cap the space heating input and by the introduction of mass. This paper reveals the full results of the monitoring and outlines recommendations for ensuring quicker response, flexibility, and efficient operation. Proper sizing of the boiler and baseboards to address recovery from setback and optimal performance is discussed. Control strategies to help prevent short cycling and enhance occupant comfort are also presented. Researchers also suggest methods for minimizing the extreme system losses identified in this study. [ABSTRACT FROM AUTHOR]

Daily hot water use is highly variable both between residences and within the same residence on different days. Determining typical hot water draw patterns to use in test procedures to rate water heaters has been difficult. Methods to compare draw patterns were developed based on data obtained from 12 separate field studies. The data set from 22,902 days in 159 houses was analyzed to determine typical inlet and outlet water temperatures. The data was then divided into three clusters reflecting house configurations that demonstrated small, medium, or large median daily hot water use. The daily hot water use within each cluster was then analyzed in terms of volume and number of hot water draws. The daily draw patterns in each cluster were also characterized using cumulative distributions for volume of draws, duration of draws, times since previous draw, and flow rates. The results of the analysis of the field data were compared to the conditions and draw patterns in the current ASHRAE method of test for rating residential water heaters. The results show a higher number of smaller draws at lower flow rates than used in the current test procedure. The results of the analysis are being considered by ASHRAE standard project committee 118.2, Method of Testing for Rating Residential Water Heaters, to revise the test procedure for residential water heaters to incorporate a range of draw patterns. [ABSTRACT FROM AUTHOR]

Residential heat pump water heaters (HPWHs) have recently reemerged on the U.S. market. These units have the potential to provide homeowners significant cost and energy savings. However, actual in-use performance of an HPWH will vary significantly with climate, installation location, HVAC equipment, and hot water use. In conditioned space, the coo ling provided by the HPWH can be either a net benefit or a penalty depending on climate; in unconditioned space the ambient air temperature has a significant impact on its performance. To determine the in-use energy consumption of an HPWH in different regions, annual simulations of 50 and 80 gallon HPWHs as well as a standard electric resistance water heater installed in conditioned and unconditioned spaces were performed for more than 900 locations across the U.S. The simulations included a benchmark home to account for interactions between the space conditioning equipment and the HPWH and a realistic hot water draw profile that varied between 45 and 60 gallons per day with local mains water temperature. Results showed that the HPWH will always save some source energy compared to a standard electric water heater, although savings vary widely with location. In addition to source energy savings, the breakeven cost (the net installed cost an HPWH would have to have to be a cost neutral replacement for a standard water heater) was also examined. The highest breakeven costs were seen in cases with high energy savings, such as the Southeast, or high energy rates, such as New England and California. Although the breakeven cost is higher for the 80 gallon HPWH than for the 50 gallon HPWH, the 80 gallon unit's higher net installed costs makes it likely that the 50 gallon HPWH will be more cost effective. [ABSTRACT FROM AUTHOR]

The B&O Bad Aibling Park, located in Bavaria, Germany, occupies a 173-acre (70 ha) facility that originally served as an airbase. Although the site buildings were in good repair, their thermal quality was poor . The district heating system was in good condition, but the scale of heat generation was too large. This project described in this paper designed a development plan that could be easily replicated and that could ultimately become a model for a zero energy city. The B&O Bad Aibling Park project employed a rich diversity of technologies that may be scaled up for application in larger urban areas. A biomass-fired boiler and a number of decentralized solar thermal facilities feed heat into an existing district heating grid in combination with grid-fed heat pumps that generate hot water individually in buildings and that use central and decentralized hot water storage tanks. This configuration allows the system to operate with low grid temperatures, and makes use of optimized energy efficiency measures while intensively harvesting solar energy. The B&O Park model project is a test bed, small enough so that it can address questions and problems in a purposeful way, yet large enough to set a standard that can be readily used in other urban areas or military installations. [ABSTRACT FROM AUTHOR]

Experiments were conducted to evaluate a multipurpose heat pump, Daikin Althermal™ split system, for its operation to provide space heating and domestic hot-water draw(DHW). The system was installed in the laboratory under controlled test conditions with all default settings specified in the manufacturer's manual. The system was first tested as a storage-type heat pump water heater according to the procedure established by the U.S. Department of Energy (DOE). Tests for combined space heating and domestic hot water were also conducted to simulate as-installed 24-hour heating demands of a single-family house in Chicago, IL, Atlanta, GA, and Houston, TX, representing cold, mixed and warm climates in U.S. The results show that the energy efficiency of the tested system were extremely low (energy factor [EF] = 0.47) when used solely for DHW heating. The average hourly system efficiencies for combined space and water heating tests were 1.54, 1.69, and 1.15 for Chicago, Atlanta, and Houston, respectively. The operating conditions and the appropriate application of this system are also discussed in this paper . [ABSTRACT FROM AUTHOR]

Combustion oscillations commonly occur in boilers, furnaces, and water heaters. At the present time, there is no systematic process for diagnosing the probable cause of an instability and solving the problem. Moreover, few design guidelines have been presented in the literature for avoiding thermo-acoustic instabilities before they occur. The current paper details steps that can be taken to prevent and diagnose combustion instabilities from the early stages of the design process through production. [ABSTRACT FROM AUTHOR]

In recent years, interest in heat pump water heaters as energy- and cost-saving devices has increased, corresponding with a recent surge in available heat pump water heater products. While a traditional electric resistance tank heater can offer a theoretical maximum COP of 1, heat pump water heaters can deliver several units of heat energy to water for every unit of electrical energy used by the system. Heat pump water heaters have, in particular, sparked the interest of electric utility companies, who see them as a potential energy-saving and peak load-reducing asset. However, modern heat pump water heaters have limitations. They generally rely on electric resistance heat to provide backup during large loads and when ambient temperatures are low. Water heaters using CO2 as a refrigerant have addressed some of these issues, but have yet to emerge in the United States for a variety of reasons. This paper describes modeling of heat pump water heater systems, including a potential next generation of systems using variable speed compressors to eliminate the electric resistance element in R134a systems. A high level of detail is required in order to evaluate the performance of different systems and control strategies, thus the heat pump cycles were modeled at the component level using a commercially available equation solving tool. In this work, a vapor compression cycle using R134a and fixed-speed compressor was modeled as well as an R134a heat pump with a variable-speed compressor and a CO2-transcritical variable-speed heat pump. The heat exchanger geometries, heat transfer and pressure drop correlations, and compressor and fan efficiencies were all considered based on available manufacturer data. A transient simulation software tool is used to simulate the weather, building, and water tank and is coupled with the vapor compression cycle model in order to simulate system performance over time. This paper details the modeling approach and simulation results for several heat pump water heater designs which use a variety of control algorithms and operate in several climatic conditions. Initial results show good agreement between the model's predictions and actual field test data recorded by the project's sponsors. The paper identifies numerous control algorithms and system configurations which offer potential energy savings and also quantify the potential advantages of using a variable-speed compressor and CO2 as a refrigerant. [ABSTRACT FROM AUTHOR]

Heat pump water heaters using CO2 as a refrigerant have been available in Japan and elsewhere in the world since the early 1990s, with many devices already installed. However, they have yet to emerge in the United States. One major reason is cost: heat pump systems will cost more than an equivalent electric resistance water heater, and CO2 systems tend to be have premium features and costs. Another reason for the lack of CO2 water heaters in the US is that existing models have differed strongly from the conventional water heating equipment seen in the US marketplace. Models developed under the EcoCute label often have an indoor tank with an outdoor heat pump, and features such as remote controls, bath water recirculation loops and others. This study examines a new, integrated CO2 heat pump water heater developed by a Japanese manufacturer and marketed in Europe, which removes many of the features common to CO2 systems and is meant for indoor, single-location installation. The integrated CO2 system was tested in the laboratory at a variety of conditions to map performance. It was tested in climate-controlled environmental chambers for a variety of ambient air conditions and also in an approximated Energy Factor test. The system tested has two modes: a comfort mode in which compressor power is high, and the system always charges to full capacity; and an economy mode in which the compressor power is low, and the system charges to full capacity during pre-set (generally overnight) hours and reheats only partially during another pre-set time period. It was tested in both modes. The system was also installed in a test home in Tennessee which features simulated occupancy and detailed data monitoring. The system was installed in the garage and allowed to run in each of the operating modes at different times. The water draw was controlled in the home to a typical load profile. This paper will outline the testing and monitoring approach. Results for both the completed laboratory testing and ongoing field testing will be shown. [ABSTRACT FROM AUTHOR]

Combustion-driven oscillations are a common problem with boilers, water heaters, and furnaces. Sound is produced by the flame and is reflected down stream from the combustion chamber. The reflected sound waves disturb the mixture flow or equivalence ratio, increasing the heat-release pulsations and the accompanying sound produced by the flame. This phenomenon has been described using a positive feedback-loop in prior work. The current paper applies the feedback- loop stability model to two boilers, which exhibited combustion oscillations. Additionally, a feedback loop model was developed for equivalence ratio fluctuations and validated. For the first boiler, the combustion oscillation problem was likely related to the geometry of the burner and the intake system, though results are inconclusive. For the second boiler, the model indicated that the combustion oscillations were due to equivalence ratio fluctuations. Accordingly, the combustion oscillations could be alleviated by changing the geometry of the intake system. [ABSTRACT FROM AUTHOR]

Independent System Operators (ISO's) and Regional Transmission Organizations (RTO's), among other activities, coordinate the buying, selling and delivery of wholesale electricity within the geographical regions that they operate. The price of wholesale energy varies by time and also by location because of the cost associated with generating and delivering electricity to different locations. Locational Marginal Pricing (LMP) is a way to reflect these locational cost differences. A number of utilities already have load control programs incorporating electric storage-type water heaters. The availability of low cost control devices, increased connectivity and emergence of energy markets has further opened avenues for peak load shifting with electric resistance water heaters. A storage-type electric resistance water heater can now communicate with a remote server which can decide on when to charge the water heater and at what rate. Various control strategies can be implemented keeping in mind the customers' needs as well as the electric grid's requirement. Storing energy in hot water when LMP's are low is one way of participating in the electricity markets for electric utilities and aggregators. A grid connected water heater that can be used to store energy in the form of hot water is tested. This paper describes the technology used within the water heater and its control system and documents the results from series of tests performed to understand the energy storage and peak load shifting capabilities. The water heater receives LMP's and day-ahead LMP's (DA-LMP) from a RTO/ISO and depending on the prices received and the charge level in the water heater, decides when to heat water. A comparison between the operating cost of regular water heater and grid connected water heater is made to quantify the peak load shifting abilities of such a water heater. [ABSTRACT FROM AUTHOR]

Gaining popularity over the past decade for gas-fired water heating, whole-house tankless water heaters have enjoyed increasing market share due to their high efficiency, relative to standard storage water heaters, the marketing of "endless hot water," and utility and government incentive programs. With this surge in popularity has come a better understanding of their performance limitations with deficiencies in the delivered-versus-rated efficiency characterized by several recent studies, due in large part to the minimum hot water draw rate requirements and startup sequence delays. While these deficiencies have been characterized sufficiently to prompt the modification of building codes, it remains a challenge to do so analytically. To better simulate the performance of whole-house tankless water heaters, building on an existing robust single node model, the authors have characterized several units with a laboratory test battery, focusing on short-term performance and intermit- tent behavior. This existing model, while complete in describing the steady-state and transient heat transfer behavior as a heat exchanger, may require additional refinement whereby some inputs may have sensitivity to test conditions (e.g,. thermal capacitance) and some impacts of tankless water heater controls are not captured, such as startup heating delays. [ABSTRACT FROM AUTHOR]

Recirculation loops (RL) in multi-family central domestic hot water (DHW) systems bring hot water close to dwelling units to provide tenants with quick access to hot water. However, long RL pipes make them a major source of system heat loss. Previous studies assessed energy savings by different RL control technologies based on measurement of overall system energy consumptions, and they did not reach definite conclusions. Overall energy consumption is affected by many operational parameters. Without evaluating RL pipe heat loss directly, energy savings cannot be accurately assessed and energy savings mechanisms cannot be well understood. This paper presents an energy flow analysis method to assess RL pipe heat loss based on field measurements of pipe temperatures and water flows. This method further separates the RL pipe heat loss into two components, one associated with the recirculation flow heat loss and one associated with hot water draw flow heat loss, so that the direct impact of controls to RL pipe heat loss was revealed. The energy flow analysis method also provided a way to characterize central DHW system performance by based on percentage weighting of four major energy flow components, including water heater loss, RL pipe heat loss, branch pipe heat loss and hot water draw energy, in the overall system energy consumption. Our field study results indicated that RL pipe heat loss represented about one third of system fuel energy consumption and the average overall system efficiency was only about 34%. [ABSTRACT FROM AUTHOR]

Cross-flow water-to-air heat exchangers are a common element in heating ventilating and air conditioning (HVAC) systems. In a typical configuration the outlet air temperature is controlled by the flow rate of water through the coil. In this configuration the heat exchanger exhibits non-linear dynamics. In particular the system has variable gain. Variable gain presents a challenge for the linear controllers that are typically used to control the outlet air temperature. To ensure stability over the entire operating range controllers need to be tuned at the highest gain state. This leads to sluggish response in lower gain states. A new nonlinear control architecture, error modulated state setting control, was used to control an experimental cross-flow water-to-air heat exchanger. The controller outperformed a properly tuned nominal PI controller for both input tracking and disturbance rejection. [ABSTRACT FROM AUTHOR]

The impact on space conditioning energy use due to operating a heat pump water heater (HPWH) inside the conditioned space is analyzed based on 2010-2011 data from a research house with simulated occupancy and hot water use controls. The 2700 ft² (251 m²) house is located in Oak Ridge, TN (mixed-humid climate) and is equipped with a 50 gallon (189 L) HPWH that provided approximately 55 gallons/d (208 L/d) of hot water at 120°F (48.9°C) to the house during the test period. The HPWH has been operated every other week from December 2010 through November 2011 in two modes; a heat pump only mode, and a standard mode that utilizes 15355 Btu/h (4500 W) resistance heating elements. The energy consumption of the air-source heat pump (ASHP) that provides space conditioning for the house is compared for the two HPWH operating modes with weather effects taken into account. Impacts during the heating and cooling seasons are compared. [ABSTRACT FROM AUTHOR]

AHRI Standard 550-590, Standard for Performance Rating of Water-Chilling and Heat Pump Water-Heating Packages Using the Vapor Compression Cycle, has recently undergone updates. The new version of this standard includes heat pump water heaters, expands the testing options for air-cooled chillers by including a barometric pressure adjustment and witness test lab requirements and provides an expanded discussion of the purpose and use of IPLV. [ABSTRACT FROM AUTHOR]

Three Heat Pump Water Heater (HPWH) units, representing the initial domestic offerings by the major manufacturers, were evaluated using a parametric test matrix. The three units tested vary in: refrigerant used, compressor size, evaporator fan size, amount of onboard electric resistance heat, condenser design, storage tank size, number and type of appliance (control) settings, and other factors that influence performance. The focus of this laboratory testing was the influence of appliance setting and hot water draw pattern on HPWH performance and efficiency, with limited variation of ambient enthalpy (within an environmental chamber), water main temperature, and thermostat setpoint. Additionally, the space conditioning effect of each unit was quantified through extended testing at stable conditions. A range of performance and efficiency was observed for each unit, both above and below results under standardized test metrics. Observations were also made of the manner in which the three HPWHs manage their thermal stores across varied demand, operational conditions, and HPWH system designs. [ABSTRACT FROM AUTHOR]

This paper explores the laboratory performance of five integrated Heat Pump Water Heaters (HPWHs) across a wide range of operating conditions representative of US climate regions. Laboratory results demonstrate the efficiency of this technology under most of the conditions tested and show that differences in control schemes and design features impact the performance of the individual units. These results were used to understand current model limitations, and then to bracket the energy savings potential for HPWH technology in various US climate regions. Simulation results show that HPWHs are expected to provide significant energy savings in many climate zones when compared to other types of water heaters (up to 64%, including impact on HVAC systems). [ABSTRACT FROM AUTHOR]

We developed a variable refrigerant flow (VRF), vapor compression, system model, which has five indoor units, one outdoor unit and one water heater. The VRF system can run simultaneous space conditioning (cooling or heating) and water heating. The indoor units and outdoor unit use fin-&-tube coil heat exchangers, and the water heater uses a tube-in-tube heat exchanger. The fin-&-tube coil heat exchangers are modeled using a segment-by-segment approach, and the tube-in-tube water heater is modeled using a phase-by-phase approach. The compressor used is a variable-speed rotary design. We calibrated our model against a manufacturer's product literature. Based on the vapor compression system model, we investigated the methodology for generating VRF equipment performance maps, which can be used for energy simulations in TRNSYS and EnergyPlus, etc. In the study, the major independent variables for mapping are identified, and the deviations between the simplified performance map and the actual equipment system simulation are quantified. [ABSTRACT FROM AUTHOR]

Thirty low-income housing units located in the high altitude San Luis Valley of Colorado received various energy conservation measures (ECM) in the summer of 2007. Measures included new furnaces, new tankless water heaters, programmable thermostats, addition/repair of roof insulation, existing furnace tune-up (where applicable), CFL bulbs and minor air sealing. Measurement and verification of the energy savings consisted of pre- and post-retrofit walk-through audits, blower door testing and temperature monitoring of select units. Verification methods consist of two whole building approach methods in addition to the calibrated simulation approach, following the ASHRAE Guideline 14-2002 protocols. All three methods are shown to produce remarkably similar savings estimates, with whole building approach methods being the simplest and least costly (time-intensive) to utilize for savings verification. The analysis provides insight into the effectiveness of the various methods as well as the impacts of the ECMs on residential energy consumption [ABSTRACT FROM AUTHOR]

A startup builder in the San Francisco Bay Area has a goal of producing factory built/modular houses with net zero energy performance. Their first prototype was a two-story, two bedroom, urban infill townhouse design. It has been in operation for roughly a year, and has been extensively measured and monitored, providing information about its net zero performance. Some technologies incorporated into this prototype include higher R value walls than typically used in this mild climate, high performance windows, excellent airtightness, a heat pump water heater, drainwater heat recovery, and a residential-scale economizer. The data collected to date indicate that the building is on track to achieve net zero performance. Several obstacles arose during the construction and commissioning of the building, which provided some useful lessons on integrating advanced technologies. Another design constraint was that the builder wished to have an all-electric house: both for 'perceived net zero performance' (all measured in electricity), and due to restrictions of California net metering laws. An analysis was conducted to assess the relative cost-effectiveness of various building enclosure and mechanical measures. The monitored data has provided a wealth of information, including submetered energy consumption for various end uses; photovoltaic system output; heat pump water heater performance, and effectiveness of the drainwater heat recovery system. It has already been used to remotely diagnose malfunctioning or improperly operated equipment. [ABSTRACT FROM AUTHOR]

In this study, the applicability of a linear input/output model to gas-fired, tankless water heaters has been evaluated. This simple model assumes that the relationship between input and output, averaged over both active draw and idle periods, is linear. This approach is being applied to boilers in other studies and offers the potential to make a small number of simple measurements to obtain the model parameters. These parameters can then be used to predict performance under complex load patterns. Both condensing and non-condensing water heaters have been tested under a very wide range of load conditions. It is shown that this approach can be used to reproduce performance metrics, such as the energy factor, and can be used to evaluate the impacts of alternative draw patterns and conditions. [ABSTRACT FROM AUTHOR]

In 2007/2008 the Renewables and Integrated Energy Systems Group at Natural Resources Canada (NRCan), a department of the Canadian Federal Government, initiated a new study of residential hot-water use with the aim of determining whether or not there had been any significant change since the last study conducted. The NRCan study utilized low-cost data loggers together with accurate flowmeters to monitor the volume of hot water drawn every two to four seconds, for a period of approximately two to three weeks, at each test site. This study monitored 38 households in the greater Ottawa area and, as such, is believed to be the largest such study of its kind conducted since the earlier work completed by Perlman and Mills (1985) or Werden and Spielvogel (1969a, 1969b). NRCan has now extended the hot-water use monitoring to other regions in Ontario, in collaboration with Union Gas, Ltd., and with the assistance of Caneta Research, Inc., adding another 36 households to the study. The new regions covered included Hamilton, London, and Sudbury. As a result of our new study, we have found that people's habits have changed and that hot-water use today is quite different to the assumptions used in the current performance test standards; for example, the total household average daily hot-water volume appears to have decreased, the average draw volume flow rates are lower, and the average number of draws per day are much greater. The authors present the results of monitoring 74 households' hot-water use and discuss the implications of these results with respect to the water heater performance test standards and the derived energy factor. [ABSTRACT FROM AUTHOR]

High-efficiency natural gas-fired space and water heating systems are an integral part of Low Energy Design, offering equipment installation flexibility at minimum operating cost. These systems are largely installed with sidewall vents in new and retrofit single family and multifamily buildings when venting through the roof is not practical, is prohibited by local code, or is beyond the maximum length of the vent system permitted by the manufacturers' installation instructions. The industry continues to investigate sidewall venting systems design and installation practices to improve building design flexibility, improve vent performance under extreme conditions, avoid nuisance outages, and avoid other occurrences such as ice formation on nearby structures. This paper investigates sidewall vent plume formation and the potential for ice formation on nearby structures in very cold climates. A review of the literature on turbulent buoyant round jet formation and transition from momentum-driven to buoyancy-driven flow is discussed as well as results of computational fluid dynamics (CFD) modeling of several geometries. CFD is a finite difference model that calculates the fluid parameters based on the physics of the fluid flow and surrounding conditions. Recommendations are made for improving sidewall vent performance and supporting flexible Low Energy Design practices. [ABSTRACT FROM AUTHOR]

The U.S. Department of Energy (DOE) recently completed a rulemaking process in which it amended the existing energy efficiency standards for residential water heaters. A key factor in DOE's consideration of new standards is the economic impacts on consumers. Determining such impacts requires a comparison of the additional first cost of energy efficiency design options with the savings in operating costs. This paper describes the method used to conduct the life-cycle cost (LCC) and payback period analysis for gas and electric storage water heaters. It presents the estimated change in LCC associated with more energy-efficient equipment, including heat pump electric water heaters and condensing gas water heaters, for a representative sample of U.S. homes. The study included a detailed accounting of installation costs for the considered design options, with a focus on approaches for accommodating the larger dimensions of more efficient water heaters. For heat pump water heaters, the study also considered airflow requirements, venting issues, and the impact of these products on the indoor environment. The results indicate that efficiency improvement relative to the baseline design reduces the LCC in the majority of homes for both gas and electric storage water heaters, and heat pump electric water heaters and condensing gas water heaters provide a lower LCC for homes with large rated volume water heaters. [ABSTRACT FROM AUTHOR]

This paper provides a methodology to evaluate end use options to reduce primary energy consumption and CO2 emissions associated with buildings. First, the paper discusses alternative energy efficiency metrics, their uses, and limitations. In particular, limitations of site energy and cost as meaningful societal metrics are reviewed, along with the challenges associated with alternative metrics such as full fuel cycle energy efficiency and CO2 emissions. In addition, the paper provides a methodology and example calculations for evaluating the site energy, full fuel cycle energy, and CO2 emissions of targeted direct use options. Results of the sample calculations show that natural gas water heaters can reduce primary energy consumption and CO2 emissions significantly compared to equivalent electric resistance water heaters. Variationsin calculated reductions occur depending on the fuels used to generate electricity and region selected for analysis. [ABSTRACT FROM AUTHOR]

This paper describes results of recent laboratory tests on a variety of hot water distribution (HWD) system piping configurations and compares HWD piping heat loss to standby losses of several common water heater types. Measured UA factors are given for both ½ in. (1.3 cm) and ¾ in. (1.9 cm) nominal copper piping with various insulation levels. Effective UA factors are also given for a number of common water heater types. This work lets readers evaluate when it makes sense to have more than one water heater in order to lessen HWD system energy losses. [ABSTRACT FROM AUTHOR]