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This paper describes extensive tests performed on a 3-ton R-22 split heat pump in heating mode. The tests contain 150 steady-state performance tests, 18 cyclic tests, and 18 defrost tests. During the testing work, the refrigerant charge level was varied from 70% to 130%, relative to the nominal value; the outdoor temperature was altered by three levels at 17°F (--8.3°C), 35°F (1.7°C) and 47°F (8.3°C); indoor airflow rates ranged from 60% to 150% of the rated airflow rate; and the expansion device was switched from a fixed-orifice to a thermal expansion value. Detailed performance data from the extensive steady-state cyclic and defrost testing performed were presented and compared. [ABSTRACT FROM AUTHOR]

Lee and Braun (2008b) developed a simple approach, termed the weighted-averaging (WA) method, that estimates building zone temperature set-point variations that minimize peak cooling demand during critical demand periods. The current paper extends this approach to air conditioning power demand and presents the results of a field evaluation for a small commercial building. The WA method uses data from two or more test days to determine a near-optimal setpoint trajectory for minimizing peak demand during a demand-limiting period. Evaluation of the method was performed over a two-week test period at a small bank building located in Palm Desert, California. The first week of testing was used to collect baseline data for conventional control and data for estimating the optimal setpoint trajectory. The second week of testing was used to evaluate demand reduction and energy savings for application of trajectories determined using the WA method. [ABSTRACT FROM AUTHOR]

Dynamic cooling coil models are useful in the development and evaluation of feedback controllers and fault detection and diagnostics algorithms. Existing models in the literature are forward models, which require detailed specification of physical parameters such as geometry and material properties. On the other hand, inverse models typically require measurements and parameter estimation techniques to identify unknown parameters and are particularly useful for online applications where models are part of a control and/or diagnostic algorithm. This paper develops a simplified distributed inverse model for transient performance of cooling coils that is based on a forward model recently presented in the literature. The inverse model employs lumped parameters for conductances and capacitances. Simple empirical forms are employed for characterizing the impact of flow rates on airside and water-side conductances. Unknown parameters are determined using a two-step approach that requires a small amount of steady-state and transient training data. Dividing the parameter estimation process into two separate steps greatly reduces the training data requirements. A case study is presented for an 8-row cooling coil that was tested in a laboratory environment. The case study highlights the ability of the model to extrapolate performance when trained with a limited amount of data. [ABSTRACT FROM AUTHOR]

Typically, catalog information for cooling towers is available only for a limited range of operating conditions for sea level applications. The information is often not suitable for the selection of a tower at other operating conditions (e.g., high altitude, different ambient temperatures), the evaluation of measured performance, or the simulation over a wide operating range. The analogy approach (Braun et al., 1989) provides a general method for representing the performance of cooling towers over a wide range of conditions. The accuracy of this methodology is 2% compared to catalog values. The methodology is able to extend catalog information to other operating conditions, including water inlet and entering temperatures, wet bulb temperature, air and water flow rates, and altitude. [ABSTRACT FROM AUTHOR]

A simple control method was developed by Braun (2007) for cool storage systems having real-time pricing (RTP) of electricity and shown to yield annual operating costs that are within about 2% of those determined for optimal control. The primary goal of the work described in this paper was to evaluate the operating cost savings associated with employing the strategy developed by Braun (2007) as compared with using chiller-priority control. In addition, operating cost savings associated with employing ice storage in combination with RTP rates were evaluated for both the near-optimal and chiller-priority strategies. For a range of systems employing ice storage with RTP rates, the cost savings associated with the near-optimal strategy compared to chiller-priority control were found to be as high as 60% with typical savings between 25% and 30%. These savings are much more significant than savings associated with employing near-optimal control for cool storage systems when typical time-of-use utility rates are employed with demand charges. A similar level of savings was determined when comparing costs for the near-optimal control strategy applied to ice storage systems with costs for systems not employing cool storage. However, relatively small savings were determined for use of ice storage when chiller-priority control is utilized. In many situations, the use of storage with chiller-priority control can actually result in higher costs than without storage. It can be concluded that chiller-priority control should not be employed in combination with RTP rate structures for cool storage systems. [ABSTRACT FROM AUTHOR]

A methodology for calibrating simulation models for use in evaluating demand-controlled ventilation (DCV) retrofits in small commercial buildings was developed. The method uses a calibrated building simulation model developed through the process of tuning individual component models (such as HVAC equipment performance) from field data. Specific parameters tuned using field-collected data were the occupancy schedules for weekday and weekend periods, ones that characterize the heating, ventilating, and air-conditioning (HVAC) equipment performance, and several key parameters characterizing the building thermal performance. The tuning of parameters associated with the CO2 modeling and occupancy included in this evaluation was described in separate publications. The tuning parameters were chosen because they were found through parametric studies to have a large influence on the economics of DCV and because they are difficult to determine from site inspections. The method was applied to several small commercial buildings located in different climates within California. The influence of the amount of training data was studied, and it was found that only a few days of training data are sufficient to develop models for evaluation of DCV retrofits. Overall improvement in the root mean square error (RMSE) of predicted hourly cooling system energy usage resulting from calibrated simulation models compared to using an untuned model with best engineering estimates ranged from 0.13 to 1.2 kWh for the test sites, with an average improvement of 27.6%. Economic benefits of DCV were evaluated against the case where outdoor airflow rates equaled those specified in ASHRAE Standard 62.1. Estimated simple economic paybacks for retrofit of DCV at the field test sites ranged from less than one year to about five years. Key factors in determining the economic benefits were the climate type and the number of HVAC units installed at a site. [ABSTRACT FROM AUTHOR]

In contrast to critical systems, one of the primary consequences of faults in HVAC&R systems is economic rather than safety related. Therefore, fault detection and diagnosis (FDD) systems applied to HVAC systems should be assessed based on economic considerations. However, existing FDD research in HVAC applications has mainly focused on technique development and validation. This paper addresses the economics of FDD application to rooftop air-conditioning units (RTUs). Two major aspects of savings associated with FDD application to RTUs are investigated qualitatively and quantitatively: service and operating cost savings. Automated FDD reduces service costs due to reduced preventive maintenance inspections, fault prevention, lower-cost FDD, better scheduling of multiple service activities, and shifting service to low season. Operating cost savings consist of utility cost and equipment life savings. Based on these two major savings, a methodology is presented for evaluating the cost savings for application of automated FDD to RTU. Application of this methodology to a number of sites in California showed that $30/kW year, around 70% of the original service costs, can be saved, and the operating cost savings range from $5 to $51/kW year depending on the location and application. The savings are significant, and the payback period for an FDD technique presented by Li and Braun (2007a, 2007b) that relies on low-cost sensors is less than one year. [ABSTRACT FROM AUTHOR]

This paper evaluates the potential for cost savings associated with the use of a near-optimal control strategy for electrical demand limiting in hybrid chiller plants. The control strategy includes the effects of electrical and gas energy, electrical demand, and chiller maintenance costs. A demand constraint is set for each month based upon a heuristic strategy, and an energy/maintenance cost optimal strategy that attempts to satisfy the demand constraint is applied for cooling tower and chiller control at each decision interval (e.g., every five minutes) throughout the month. Evaluation of the strategy was performed using a simulation tool that predicts the utility costs associated with hybrid plants. Annual cost savings associated with employing demand-limiting control for hybrid cooling plants were evaluated for a wide range of conditions. Costs can be reduced by up to 50% compared to a strategy that is just based on minimizing energy costs. The cost savings for demand-limiting control generally increase with increasing ratio of demand to total utility costs. In addition to depending on utility rates, the ratio of demand to total costs depends on the load profile. In general, the use of hybrid cooling plants with demand-limiting control is more beneficial for buildings with shorter occupancy periods having high demand charges. Buildings with shorter occupancy have a higher ratio of peak load to integrated load. [ABSTRACT FROM AUTHOR]