Reverse Cycle Chiller Application in Multifamily Dwelling
Domestic Water Heater for Multifamily Dwelling: Reverse Cycle Chiller vs. Conventional Electric
A chiller that operates the refrigeration cycle in reverse in order to provide domestic hot water; also known as a heat pump water heater.
Item ID: 233
Water Heating--Water Heaters
Technical Advisory Group: 2010 HVAC TAG (#3)
Average TAG Rating: 2.8 out of 5
TAG Ranking Date: 06/29/2010
Reverse Cycle Chillers (RCCs) are a form of air‐to‐water heat pump technology that can produce hot water nearly three times more efficiently than electrical water heating. Although in common use in warmer climates for both cooling and hot water production, RCC technology has limitations in our climate region due to our relatively cold winter weather and the relatively small need for cooling. Analyses performed by Ecotope for regional conservation programs indicate that for multifamily buildings, production of domestic hot water accounts for approximately 25‐30% of the residential energy use (Heller 2008). Reverse Cycle Chiller (RCC) technology is poised to emerge as a way to significantly reduce energy use for hot water systems in multifamily buildings.
BPA is conducting field tests of reverse cycle chillers in multi-family applications where the heat pump extracts energy from an underground garage exhaust system and uses it to provide domestic hot water. In this application, performance should show an improvement as the below-grade garage ambient temperature is insulated from cold outside weather.
Baseline Description: Electric water heater
Baseline Energy Use: 3.5 kWh per year per square foot
Regional water heater consumption for single-family homes is about 3,030 kWh/year for about 2.2 people per site (Ecotope, Inc., "Residential Building Stock Assessment: Metering Study", prepared for the Northwest Energy Efficiency Alliance, April 28, 2014). We don't have similar metered data for multi-family residences, but with an average of 1.92 people per unit, and assuming a linear relationship, we obtain an estimate of 2,644 kWh/year. (Note: This estimate probably overestimates water heating energy usage due to a higher population of children in single family houses). With an average unit size of 766 sf, we obtain an hot water energy use estimate of 3.45 kWh/sf.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 40%
Low and High Energy Savings: 10% to 60%
Energy Savings Reliability: 3 - Limited Assessment
Depending on climate, the efficiency of heat pump technology can offer a significant energy savings.
Energy Use of Emerging Technology:
2.1 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
To get the maximum technical potential for retrofit applications in the Northwest, assume that this would mostly be installed in units that already have electrical central domestic hot water systems (DHW) (Baylon, 2013 Pg 48-49, Tables 44 & 45). This is done per square foot of living units served, since the size of the systems will vary with the size and number of units being served.
Electric Central Domestic Hot Water Systems (DHW) in Multifamily Units
Regional Technical Potential:
| Population || Avg. sf per unit || Total sf. || % Central DHW || % Electric || SF Elect. Central DHW |
| 863,104 || 766 || 661,137,664 || 11.2% || 20.4% || 15,106,000 |
0.02 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $1.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.10
Baseline Technology Unit Cost (Equipment Only): $0.50
The cost for a RCC system in a new 163-apartment building designed for construction in Seattle was $110,275. This represents a cost of $677 per apartment. (See Citation #1)
Simple payback, new construction (years): 4.0
Simple payback, retrofit (years): 8.7
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
The cost effectiveness of this technology is dependent on the specific application. For instance, installing the system in a large facility will have a quicker payback than an installation in a much smaller one. A feasibility study funded by BPA reports a projected simple payback of 5 years for an installation in a 163-apartment building (see Citation #1).
A reverse cycle chiller (RCC) is a chiller that operates the refrigeration cycle in reverse. RCC is also known as a heat pump water heater. The RCC uses refrigeration technology to heat water by extracting heat from the ambient air. This water is then fed to one or more storage tanks and then used for domestic hot water and/or process heating water. This technology is similar to heat pumps used for space heating and cooling. The main difference is that in this application, water is heated instead of air.
The most common standard practice is to heat water for domestic and/or process heating using natural gas or propane water heaters, electric water heaters, or gas or electric boilers.
RCC equipment has been in use in warm climates for over 20 years, but has not taken root in the Pacific Northwest because RCC performs poorly in climates with cold winters. Manufacturers are beginning to develop RCC equipment that performs well in cold conditions, which will help this technology’s adoption in the Pacific Northwest. Ecotope, in Seattle, Washington, has completed a feasibility study of the technology for BPA. A link to the report for this study can be found in the Citations section of this form (1)
End User Drawbacks:
Human factors present a barrier to rapid widespread adoption of this technology in multifamily buildings. This issue primarily centers on the fact that this is a new application that few in the region are familiar with. Designers, installers, and developers are all historically reluctant to be the first to try to incorporate new technologies into their projects. One major advantage to individual electric water heaters in apartment units is that they are extremely simple and are a well‐understood technology. This proposed technology requires more engineering design and a higher level of installation expertise than traditional electric water heaters.
Operations and Maintenance Costs:
Baseline Cost: $1.00
per: square foot per year
Emerging Technology Cost: $1.00
per: square foot per year
A straight cooling chiller and a reverse cycle chiller require the same maintenance.
Anticipated Lifespan of Emerging Technology: 15 years
The useful life for RCC equipment is difficult to assess. The manufacturers interviewed for the BPA feasibility study all claimed typical useful lives of at least 20 years (See Citation #1). Some acknowledged that the compressors have a typical lifespan of about 15 years, but can be readily replaced. There are also some smaller parts that can be replaced, if necessary, without significant impact on the overall system. Some manufacturers noted that they have had this type of equipment in service for upwards of 40 years in some cases. 15 years is a reasonable expectation for the effective life of this product.
The life of the equipment may be largely a function of water quality, which impacts any technology for this application
A competing technology is variable refrigerant flow (VRF – see ID #126). VRF can have multiple zones on a single outdoor heat pump. One of the zones can be for hot water. See pages 37-39 at (Mitsubishi, 2011)
Also, found at (Mycom, 2013) is a CO2 heat pump called the “ECO-CUTE”.
Lastly, another option is individual heat pump water heaters in each unit (see ID #172)