Domes Energy Retrofit

The UC Davis Domes, built in 1971, were originally envisioned as an economical, eco-friendly, living solution for UC Davis students. Situated across Hwy 113 from the UC Davis West Village Zero Net Energy community their unique dome-shape silhouettes create an excellent counterpoint of sustainable living, old vs. new.

Domes location

UC Davis Domes location (left) and Site Plan (right)

In 2012, the UC Davis Program for International Energy Technologies (PIET) began to work on the Domes Zero Net Energy (ZNE) project with the objective of demonstrating the role of community-scale projects and resident involvement to promote zero-net energy technological and behavioral strategies. Evangeline Zhang authored a follow-up report that detailed the results of the retrofits done as part of the ZNE project

The Path to ZNE

For the Domes ZNE project, the team followed the “path to ZNE” approach, a methodology developed by PIET to address zero net energy projects for buildings and communities. This methodology was developed not only for projects intended to achieve energy neutrality, but also for those aiming at significantly reducing the total energy consumption. Read more about the Path to ZNE.

Understand baseline

End use breakdownUsing the “Path to ZNE” approach, the team’s initial work focused on establishing a baseline for energy-related services, to understand the impact of the different end uses of energy. A baseline analysis was then conducted by using a combination of methods to obtain the different inputs required. These methods included: review of historic energy consumption data (from the single meter existing in the complex), on-site observations and measurements, surveys and interviews to residents and maintenance managers. The baseline analysis suggested that the largest end uses or energy at the Domes were domestic hot water heating and space heating.


Initial Building envelope and energy efficiency measures

The next stages in the “Path to ZNE” approach include the study and implementation of building envelope improvements and energy efficient equipment alternatives to address the largest energy end uses identified in the baseline analysis. Based on this, the focus of these stages was on reducing the space heating load, by reducing heat leaks, and reducing the energy used for domestic hot water heating, by using a more efficient technology to heat the water. To reduce heat leaks, three measures were proposed: replace the old wall/roof insulation by new one, replace windows, skylights and doors by new ones with improved thermal properties, and insulate the concrete floor slab outside perimeter. For the water heater, a cost-benefit study of efficient alternatives concluded that a heat pump water heater (air-source heat pump) was the most convenient option to replace the existing electric storage water heater. Envelope measures were implemented in two domes (7 & 8) and a heat pump water heater was installed in one dome (8). These two domes were already being upgraded to become ADA[1] compliant.


Left – Dome 8 after retrofits. Right – Heat pump water heater installed in Dome 8.

Monitoring of initial retrofits

Data loggers were installed in two un-retrofitted domes, to validate the baseline analysis, and in dome 8 (retrofitted), to measure energy savings due to the implemented retrofits (insulation, windows, doors, skylights and heat pump water heater). Data points measured included electricity consumption at each circuit breaker, indoor/outdoor temperature and relative humidity, domestic hot water temperature and usage.


Left – Testing monitoring equipment in the lab. Right – Installing monitoring equipment

Preliminary results verified the initial findings of the baseline analysis and suggested a reduction in the energy use for domestic hot water of approximately 50%. Some energy savings were also shown for space heating, but the percentages in this case are still unclear. Values still need to be refined by incorporating the latest data to the analysis in order to make quantitative statements on the effect of both the envelope and water heater measures.

ZNE Retrofit PG&E grant

Learnings from the baseline analysis and the initial envelope and energy efficiency measures study, led PIET’s team to write a proposal to PG&E to conduct further research on ZNE strategies at the Domes.  A grant was awarded to:

  • Design and install prototype packaged terminal heat pumps utilizing drilled horizontal geothermal heat exchangers to improve the level of service to 2 domes, which were served by an electric resistance space heaters each.
  • Install an air-source packaged terminal heat pumps to improve the level of service to 1 dome, which was served by only an electric resistance space heater.
  • Install a heat pump water heater to serve 3 domes via a district loop and replace the existing electric resistance water heater at each dome.
  • Collect and analyze detailed energy data through instrumentation of equipment, zone and exterior conditions.
The proposed equipment were commissioned in early February 2014 and collected data – which is ongoing – was utilized to assist a simulation and market study for evaluating the feasibility of large-scale, commercial deployment of the prototype terminal heat pumps utilizing the drilled horizontal ground loop in two building archetypes: medium-density commercial lodging (small hotels, motels) and residential multifamily (low-rise apartments). The report of this study may be requested from PG&E.

Technology Descriptions

Heat pump water heater (HPWP)

A heat pump takes advantage of the thermodynamic properties of organic fluids (refrigerants) which allows the system to provide a certain amount of cooling or heating with less energy input relative to an electric resistance heater where the input electrical energy is directly converted to heat in a 1:1 ratio. When an air-source heat pump is applied to water heating service, significant improvements to electrical energy use efficiency can be achieved, except when the outdoor air temperature is very low. Capacity and efficiency of the heat pump is greatly reduced at low outside are conditions which forces the back-up resistance heater to operate.
Ground-source heat pump (GHP)

A GHP system takes advantage of the ground’s moderate temperature to heat or cool air or water very efficiently. A study was conducted at the Domes, to evaluate different types of GHP systems. Options analyzed included both central and individual configurations, providing either all or some of the services of space heating, space cooling and domestic hot water (the most significant end uses in terms of energy consumption).

From the study, an individual GHP system providing space heating and cooling to a single dome was selected for installation at the Domes. The system comprises of a prototype heat pump unit, called GTHP, which was modified from a commercially-available air-source heat pump unit (known as PTHP). The GTHP utilizes a shallow, horizontally drilled geothermal heat exchanger.

[1] The Americans with Disabilities Act (ADA) ensures, among other things, access to the built environment for people with disabilities through standards for construction and alteration.