Christian K. Bach

Water-based thermal energy storage (WTES) can be used to shift peak heating and cooling loads in residential buildings and adapt to electrical grid conditions in order to accommodate more renewable energy into the grid. This study examines the performance of a heat pump in cooling mode when integrated with a WTES using TriCoilTM, a novel three-fluid fin and tube heat exchanger, as indoor coil. This manuscript focuses on evaluating the system's effectiveness in maintaining thermal comfort in the conditioned space during discharging the WTES. The system is operated using a supervisory control model with predetermined hours for charging and discharging the WTES. We used a simplified building model that, coupled to the system model, predicts zone temperature and humidity. We conducted simulations of typical peak summer days and whole summer season in two locations of the US- Stillwater, Oklahoma and Phoenix, Arizona. The thermal comfort in the conditioned space is quantified using the predicted mean vote (PMV) for a thermostat setpoint of 23 °C. In both locations, the PMV stays within the neutral comfortable range of 0.5 to -0.5 throughout the cooling season with humidity generally maintained below 60% relative humidity. We also assessed the system's potential for reducing electricity costs through load shifting, by charging the WTES during off-peak hours for use in on-peak hours. The reduction in total electricity cost in Stillwater between June 12th and September 22nd was 11% for 75% of the on-peak hour load shifted to off-peak hours. In Phoenix, the WTES was able to shift 80% of the peak hour load and reduce total electricity cost by 16.1% between June 1st and September 30th. Finally, we investigated the impact of the maximum WTES discharge temperature on space humidity, thermal comfort and system operation by varying the temperature between 13 °C and 16 °C.

Accurate performance measurements of equipment in the laboratory requires air mixing to reduce temperature and humidity measurement error. The National Bureau of Standards (NBS), now known as National Institute of Standards and Technology (NIST) conducted in-depth experimental research on the static air mixing devices in the late 1960s, which remains the most comprehensive work in this area. Today, very limited guidelines are available for air mixers, with ASHRAE RP-1733 addressing this gap. In this paper, computational fluid dynamics (CFD) analyses are presented to quantify the performance of candidate air mixers for RP-1733. It was found that the proposed static air mixing models, consisting of louvers with and without baffles as well as orifice and orifice-target combinations, add turbulence to the airstream, enhancing the mixing process. It was observed that the louver-baffle, orifice, and orifice-target mixer have greater pressure drop than louver mixers with only a negligible increase in mixing effectiveness. Therefore, the louver mixers provide a better trade-off between mixing effectiveness and pressure drop.

For measurements of unitary HVAC&R equipment and heat exchanger measurements, tolerances on capacity measurements relative to the published ratings or mismatch in energy balances are limited to 5% as mentioned for AHRI standards (210/240, 340/360, and 365), ASHRAE 33 and 37, and in US federal regulations (US DOE, 2017). However, differences in design of the air mixing and measuring apparatus due to generous guidelines may result in discrepancies in measured airside capacity that exceed the allowable tolerances, leading to so called “false testing failures”. In order to maintain our HVAC&R industries’ credibility it is essential to develop standardized design criteria for the test apparatus that reduce the probability of such failures. This literature review gives an overview of available and relevant research and standards to provide comprehensive and general information on air mixing devices and measurement techniques for psychrometric performance testing. Furthermore, this review article summarizes mixing effectiveness and static pressure drop for representative mixer types, design parameters, as well as various testing conditions based on our understanding of experimental results in open literature.