Davis Energy Group

HVAC Systems

Davis Energy Group has extensive experience in the evaluation of heating, cooling, and ventilation strategies. Technologies and strategies include the following:

Ground Coupled Heat Pumps

Ground coupled heat pumps utilize a ground source heat exchanger to extract heat during the winter and reject heat during the summer to provide building heating, cooling, and, in some cases, domestic hot water. Between 1997 and 1999 DEG worked with PG&E on the Geothermal Heat Pump Commercialization/Model Utility Program Demonstration, co-sponsored by the Geothermal Heat Pump Consortium and the California Energy Commission. The resulting eighteen reports addressed the design, installation, monitoring, and public awareness efforts related to several demonstration systems of varying types.The reports also included a market evaluation, feasibility studies, revision of DOE-2 modeling assumptions, analysis of alternative technology options, optimization of hybrid systems, development of Title 24 options, analysis of cost effectiveness, and suggestions for a business plan and utility program possibilities. DEG completed a 2010 evaluation for PG&E which utilized the eQUEST modeling software to evaluate the potential of ground coupled heat pumps as a strategy for zero net energy homes.

Ventilation Cooling and Residential Pre-Cooling

The problem of peak load in California prompted a study to investigate the potential for eliminating vapor compression cooling in transition climates by improving envelope design and employing nighttime pre-cooling of building mass with outdoor air. Launched in 1994 by the California Institute for Energy Efficiency under the title “Alternatives to Compressor Cooling”, the project studied the scientific, engineering, sociological, and market issues related to residential natural cooling. This research showed that carefully controlled mechanical ventilation cooling can significantly reduce summer peak load, and can eliminate the need for vapor compression cooling in areas between the California coastline and the central valley. Applications for this technology include dry climates where vapor compression cooling is needed only a few days of the year, as well as hot dry climates that have a daily dry bulb temperature range approaching 30°F (17°C), which includes much of the West, Southwest, and areas of the Northeast.

The ACC project spurred DEG’s development of the NightBreeze®, a system that integrates ventilation cooling, vapor compression cooling, heating, and fresh air ventilation system. DEG has since installed and further monitored numerous NightBreeze systems with positive results.

In a 2007 study for the Sacramento Municipal Utility District (SMUD), DEG investigated the feasibility of off-peak residential pre-cooling as a tool to limit peak demand. The study evaluated capabilities of available controls, completed computer modeling to assess potential benefits, completed field testing of promising pre-cooling strategies, and evaluated compatibility of pre-cooling strategies with the generation profile of a SMUD-owned wind generation facility. Precooling with outside air as well as air conditioning was shown to be an effective means of reducing demand while maintaining comfort and having no adverse energy use impacts.


DualCool installed on a rooftop unit

DualCool is an accessory for packaged rooftop units (RTUs), which are commonly used in low rise non-residential buildings, that evaporatively pre-cools both condenser air and ventilation air. DualCool technology was developed by DEG and spun off to Integrated Comfort Inc., who now produces it. DEG evaluated DualCool under PG&E’s Cross-Cutting Demand-Reduction Program, monitoring 27 units at six locations in northern California. DualCool was found to be most cost effective in new construction projects where it offers capacity reduction benefits, and for reducing energy use with existing systems that are subject to high loads.

Evaporative Condensers

Evaporative condenser operation schematic and AquaChill unit.

DEG has completed simulations, laboratory and field testing of a variety of evaporative condensers. With Building America support, a Freus unit was field tested in the Southern California desert town of Borrego Springs in 2006 and 2007. Performance results showed significant energy savings over standard air cooled condensing equipment. During 2009, DEG worked with Beutler Corporation (manufacturer of the AquaChill evaporative condenser) to assess AquaChill design and performance, and helped set up their in-house test facility. Potential enhancements were identified with the help of a refrigeration engineer and design variations were tested. DEG completed a 2010 evaluation for PG&E which utilized the eQUEST modeling software to evaluate the potential of evaporative condensers as a strategy for zero net energy homes, and completed an evaluation of an existing system under Building America in 2011.

Air-to-Water Heat Pumps
Air-to-Water Heat Pumps

Aqua Products air-to-water heat pump in a Tucson, AZ home and schematic of air-to-water cooling system with mixed-mode distribution.

Air-to-water heat pumps applied to mixed-mode distribution systems utilize hydronic distribution through a small fan coil connected in series with and upstream of a radiant floor system. DEG first evaluated the effectiveness of such systems in a Building America field study in Borrego Springs, CA, with results showing significant improvements in cooling efficiencies. In 2010, also under a Building America contract, two other projects were initiated to test this strategy. Both systems have been fully instrumented and are being monitored over one year to capture complete performance data over the cooling and heating seasons. Results will be used to quantify energy savings, cost-effectiveness, and system performance using different operating modes and strategies. A calibrated TRNSYS model is under development that can be used to predict energy savings in various climates.

HVAC Quality Maintenance

Research has shown that HVAC maintenance measures in residential and small commercial buildings have the potential to save 30 to 50% of cooling energy. This potential for savings has prompted utilities across the nation to include HVAC maintenance measures in their energy efficiency programs. However, evaluation, measurement and verification (EM&V) studies of these programs have shown that savings estimates based on laboratory research have not materialized. To investigate possible reasons for program deficiencies, Southern California Edison retained DEG and the Western Cooling Efficiency Center to analyze the sources of uncertainty in delivering and measuring these programs. An analysis of the uncertainties in the measurements of common variables was completed, and results were shared with EM&V teams, participants in maintenance programs, and contractors. The report identified the possible impact on ex ante savings of measurement uncertainty and recommended improved practices to reduce measurement error. This information will be useful to program planners in designing future programs.

Following on this research, DEG and the ARBI team developed an efficient procedure for quickly diagnosing HVAC system defects that is targeted at home performance contractors. A report describing this approach is being published through the Building America program.

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