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Summary
Most heating and cooling appliance test procedures measure system performance at a fixed speed, while maintaining constant specified indoor and outdoor air conditions. To better capture the actual observed field performance of heating/cooling appliances and their controls, several parties1 have developed a load-based test approach in which the indoor room is subjected to a simulated time-varying load and the equipment is allowed to respond to the imposed loads (i.e., a simulated building), while outdoor room dry-bulb and humidity are controlled to simulate the seasonal weather of a particular zone. However, these tests are difficult and time consuming to implement. The goal of the project is to develop a new approach to a test standard that provides accurate seasonal energy costs to consumers, but at a reduced cost to U.S. manufacturers of heating, ventilating, and air conditioning (HVAC) equipment.
Description
Objective
To provide the measurement science needed for input to industry-consensus standards that give more realistic seasonal performance of HVAC equipment at a reduced burden to manufacturers.
Technical Idea
Current load-based tests more accurately capture installed performance (compared to steady-state tests) but are excessively complex, cumbersome, expensive, and time consuming. The tests require dynamic control of two psychrometric chambers to emulate the indoor and outdoor weather conditions. The outdoor chamber, containing the outdoor portion of the HVAC system, simulates the weather of a given climate zone, and tests are typically conducted at 10 to 11 steady temperature/humidity test conditions to capture the HVAC system response to a particular weather zone. The indoor chamber contains the indoor part of the HVAC unit and emulates the dynamic temperature and humidity conditions inside the building in response to the HVAC system capacity and the thermal load of the building envelope, based on a validated computer model of the building. The HVAC equipment activation is regulated by the connected thermostat (located in the indoor chamber), and so the controls are evaluated under more realistic dynamic conditions that mimic the indoor and outdoor conditions. The environmental chambers housing these load-based tests must have tight dynamic control of dry-bulb temperature and humidity to accurately provide the varying conditions throughout the diurnal simulation. Air temperatures and air flow velocities around the thermostat must be monitored and controlled carefully to mimic actual conditions for a typical residence. Multiple dynamic tests are combined to produce a seasonal efficiency rating based upon results from all the data. Designing and operating psychometric chambers to achieve these varied and tightly controlled conditions is difficult and expensive, so there is a need for a test procedure that is simpler but still captures the performance of the equipment and controls under real-world conditions.
The new idea in the proposed work is to greatly reduce the number of required tests and their complexity by first obtaining a performance map of the response of the HVAC unit itself to given representative indoor and outdoor conditions. It is believed that with a much smaller number of select test conditions, an accurate performance map can be developed which can then serve as an empirical model of the HVAC unit to be used in the load-based test procedure much as the building model is now currently used rather than testing in an actual building. Substituting empirical performance maps of the HVAC equipment for the actual equipment has a high probability of success since NIST has routinely developed performance maps of HVAC equipment and then implemented them in predictions of the seasonal performance of the HVAC equipment in the NIST Residential Test Facility, with good accuracy2. The only remaining unknown component of the HVAC unit’s performance is then the response of the thermostat, and more importantly, the control algorithm in the thermostat, to the indoor/outdoor conditions of the chambers. Hence, the thermostat and its control system will be placed in the indoor chamber and together with the performance map of the HVAC system, the building model, and the weather data providing the outdoor chamber test conditions, an accurate seasonal response of the HVAC system should be obtainable for the same conditions as the full load-based testing. The indoor chamber to house the thermostat for the dynamic load-based testing can then be much smaller, more accurate, and less expensive than an entire set of dynamic chambers built for the capacity of the HVAC unit, and the tests for the HVAC system performance maps can be done in traditional steady-state chambers in one day or less depending on the complexity of the HP/AC being tested (single-speed, multi-speed, variable-speed, etc.).
The ability of manufacturers to more routinely test their systems and control algorithms will allow them to optimize them for improved performance.
Research Plan
The first task will be to familiarize researchers with the existing international load-based test methods through review of the test procedures and a literature review of the technical papers that lead to the standards. Then, the chambers will be configured for typical load-based tests and integrated with the computer models to simulate the building load. Next, load-based tests will be run and analyzed per the existing CSA standard and used as a baseline for evaluating the novel test methods. Further, these initial tests will be used to identify opportunities for simplification in the test procedure, the accuracy of the tests, and the necessary suite of steady-state tests required for a HVAC system performance test. The chambers will then be run in simpler steady-state mode to obtain the HVAC system performance map. The thermostat will be installed in the indoor chamber, the HVAC system performance map will be implemented in the building model controlling the indoor chamber, and the load-based test will be repeated in the simpler thermostat/control system configuration. The data from these tests will be reduced and analyzed to determine the efficacy of the new approach, in comparison to the existing load-based test standard. The tests will be optimized and repeated as necessary for accuracy and understanding. Finally, a new standard test method will be developed, and we will work with industry-consensus standards organizations to implement the simpler U.S. standard to replace existing, complicated ones.