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Space heating and cooling use represents about 40%-50% of total annual energy and is usually the highest end use in homes. Therefore, matters impacting space conditioning may have significant impact on home energy use. Correct refrigerant charge, preventative maintenance, and air distribution duct location, design, airtightness and insulation integrity can have significant impacts upon energy use. Inadequate duct design and installation can result in elevated total external static pressure, which can have significant impacts on performance. This research project was designed to investigate the cooling performance impacts of increased static pressure, which often results from poor design and installation practices. Two identical university lab homes sited next to each other were used with a metal duct system in one home and a flex duct system in the other. Each duct system had the same general layout within a vented attic. Space conditioning was provided by identical two-stage split-DX heat pumps having the same model numbers. The air handlers used electronically commutated motors that delivered design airflow across a wide range of static pressure. Energy use, temperatures and relative humidity and refrigerant line temperatures and pressure were monitored. An initial test 1 compared quality duct design, sizing, and installation meeting industry standards for each duct type. The metal duct system at 0.34 in WC (85 Pa) was used as a baseline of comparison to the flex duct at 0.44 in WC (110 Pa). Two additional tests were run with the flex system at higher static pressures. Test 2 operated the flex system at 1.00 in WC (249 Pa), which represented high compression and some poor radius turns. Test 3 operated the flex system at 0.82 in WC (204 Pa), which represented more typical installation practice. There were significant central fan energy impacts. Observed impacts of duct static pressure upon the ECM fan energy found flex duct energy increases of 33%, 148%, and 72% for tests 1, 2, and 3 respectively. This paper further discusses a comparison of the daily cooling energy impacts by condensing unit and air handler fan for typical summer days as well as an annual energy impact between the metal duct and 0.82 in WC (204 Pa) flex duct for three different locations in climate zone 1 and 2. Implications of over-compression of metal duct exterior FSK insulation wrap upon energy was also discussed. [ABSTRACT FROM AUTHOR]

Dehumidifiers (DHUs) are the second most-selected equipment, after air conditioning (AC), used to manage indoor relative humidity (RH) in homes. They can offer the lowest first-cost, are well-established in the market, and are often easier to install than other supplemental dehumidification alternatives. However, DHUs have the potential to use significant amounts energy and may impact the performance of the central ducted cooling system under certain conditions. Dehumidifiers may be designed to be ducted or un-ducted. Dehumidifiers with ducts are sometimes referred to as whole-house or ducted dehumidifiers. Manufacturer manuals offer several different options for ducting DHUs, but they do not provide adequate information about potential performance impacts. Also sorely missing are expanded DHU performance metrics to help professionals and consumers determine the appropriate DHU capacity and to help predict operational efficiency for specific realistic applications. The Florida Building Commission initiated a research project to determine if some common ducted DHU configurations had significant energy and moisture impacts and whether any configurations should be not allowed in Florida Building Code. The research evaluated measured energy use and latent heat removal rates of AC and DHU for four different common ducted DHU duct configurations. Testing occurred during variable weather and interior latent loads common in a warm moist climate. A highly-instrumented building lab was used to evaluate AC and DHU performance based upon how a DHU was ducted to a central AC ductwork and compared these to a DHU ducted to and from an open central room. There was less than 1% difference in annual space conditioning energy (DHU + AC) among two different methods of DHU ducted to the central supply duct and the DHU ducted directly to indoors. However, steady-state and longer-term test findings showed that a DHU ducted to and from a central cooling system return upstream of the central cooling evaporator coil resulted in the annual predicted space conditioning energy use of 308 kWh/year (4%) more than the DHU ducted directly to indoors. It also resulted in decreased central AC latent performance by 28% when the DHU and AC ran simultaneously. This DHU duct configuration further degraded dehumidification performance by causing moisture to be evaporated off of the central cooling coil at a rate as high as 2-3 pounds of water per hour when the AC was cycled off and DHU operated. This paper discusses the experimental method, results and recommended practice of ducting DHU for optimum performance. [ABSTRACT FROM AUTHOR]

Mechanically distributing an appropriate amount of outside air (OA) ventilation throughout a commercial building with variable occupancy can be challenging without over-ventilating, and can have significant energy costs associated. This particularly tests engineers that seek to optimize energyefficiency with effective variable OA throughout different zones. Conditioning OA in hot-humid climates takes special consideration due to the very high latent loads that must be removed. Simple HVAC systems must constantly operate the supply fan to meet ventilation requirements, even if indoor comfort temperature has been met. This method of operation can result in high indoor humidity during periods of low cooling load. It may also result in over-cooling if the setpoint is lowered to increase dehumidification, particularly with conventional packaged and split HVAC systems. Using a dedicated outside air system (DOAS) to handle 100% of the ventilation air has been part of the solution to improve moisture control and overcooling issues. This improves comfort control by dedicating systems properly sized solely for heating and air conditioning (HAC) loads, and dedicating DOAS specifically sized for the OA ventilation load. It can also make it easier to distribute variable amounts of OA to different zones. While DOAS help improve control, there are still challenges to managing energy-efficient OA conditioning and distribution in buildings with variable cooling loads and occupancy. Many packaged DOAS use air distribution fans that operate at constant speed and vary airflow by simply using air damper controls. Fixedflow designs have more limitations to energy savings potential than variable supply flow DOAS. The advancement of variable speed fan motors and variable refrigerant flow technologies have made their way into space conditioning systems and offer good energy savings potential as they can operate very efficiently at varying load levels. These advancements had recently been developed and applied to a package DOAS, and a field study was completed through third-party evaluation. The variable-capacity DOAS was put into a field trial at a high school cafeteria. Testing showed that the unit was able to deliver 55°F-60°F (12.8°C-15.6°C) dewpoint supply air under a variety of weather conditions and at variable ventilation rates. Analysis indicated a potential 77% reduction in annual DOAS energy when a schedule-based controlled fixed-flow DOAS (EER=10) was replaced with the variable capacity DOAS unit using CO2 demand-based control. Demand control accounted for about 36% of the total savings. [ABSTRACT FROM AUTHOR]

Field research performed in 70 central Florida homes found that return grilles are almost always located in the central zone of the house and that individual rooms rarely have ducted return air or return transfer pathways. When interior doors were closed, the closed rooms went to +0.0249 inches of water gauge (in. w.g.) (+6.2 pascals [Pa]) wrt outdoors (wrt = with respect to), and the central zone went to -0.0116 in. w.g. (-2.9 Pa) wrt outdoors. Room pressures as high as +0.150 in. w.g. (+37.3 Pa) and central zone pressure as low as -0.059 in. w.g. (-14.7 Pa) wrt outdoors were found. These pressures create exfiltration from the closed rooms and infiltration in the central zone. With the air handler operating, the house infiltration rates increased, on average, from 0.46 to 0.60 air changes per hour (ach) when all interior doors were closed. According to homeowner reports, interior doors are closed 11% of the time, on average. These pressures and increased infiltration rates impact indoor air quality, indoor relative humidity, energy use, peak electrical demand, comfort, and system sizing. [ABSTRACT FROM AUTHOR]

Research in 88 central Florida commercial buildings during the last decade has found that 26% of the air distribution systems had substantially unbalanced return air. Unbalanced return air occurs when there is a restriction to airflow between the supply discharge and the return air, creating positive and negative pressure fields throughout the building. Severe consequences in commercial buildings can occur as a result of unbalanced airflows. This paper examines unbalanced return air and its consequences in three commercial buildings and explains why balancing airflow in buildings is a critical part of maintaining a healthy and energy-efficient building. [ABSTRACT FROM AUTHOR]