Residential Scale Combined Heat and Power (CHP)
Residential Scale Generator: Combined Heat and Power (CHP) vs. Grid Supplied Power
Residential scale fuel-based electrical generators that recover excess heat so it can also be used to produce hot water, space or pool heating.
Item ID: 73
Power Systems--Power Generation
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2014 Residential Building TAG (#10)
Average TAG Rating: 2.5 out of 5
TAG Ranking Date: 04/10/2014
TAG Rating Commentary:
- 50% energy savings? Of course I'm interested. Cost may be prohibitive but this might be a great chance to explore another big changing technology. Seems unlikely that this would be made code for a long time and could be used by efficiency programs to fulfill efficiency needs.
- The waste heat recovered isn't worth the fuel consumed to recover it. We need to move away from fuel-based generators as quickly as possible.
- This is not an electric savings measure - it is fuel switching
- May be useful in a few situations. Adds a level of complexity that may not be welcomed. Not clear that there's much absolute energy savings potential when comparing it to a 95% efficient gas furnace or boiler. From an electricity point of view, it isn't an efficiency measure, it's a switch in means of generation.
Residential scale Combined Heat & Power (CHP) is the simultaneous production of heat and electricity in individual homes. Effectively the CHP unit can replace the gas central heating furnace and provide heat and hot water, while additionally providing the majority of the home's electricity needs. Recovered heat can be used for space heating, hot water, spa, or pool heating needs. Typical residential CHP plants produce from 1 to 5 kW of electrical output.
Although individual residential CHP units produce relatively small amounts of electricity, the significance of residential CHP lies in the potentially huge numbers of systems which may ultimately be installed in millions of homes.
Electrical generation is proportional to annual operating hours. System efficiency is maximized when electrical generation is a secondary product with the unit running to meet space or water heating requirements. These units could also be used to produce energy during peak periods when served by utilities offering "time of day" rate schedules. The "best" operating scheme is dependent upon the differential cost between electrical energy and natural gas cost.
Manufacturers of residential scale natural gas-fired CHP systems including Freewatt (using a Honda engine) and Marathon Ecopower. WhisperGen is a 4-cylinder double acting Sterling engine sized for residential applications. A 2 kW Ecopower Marathon engine can provide about 13,000 Btuh of recoverable thermal energy. Residential scale Freewatt and Ecopower units have been marketed and installed for a number of years. Both are supported by utility incentives in areas where they actively market their products.
Baseline Description: Grid powered home
Baseline Energy Use: 6.8 kWh per year per square foot
The 2011 NEEA "Residential Building Stock Assessment: Single-Family Characteristics and Energy Use" study indicates an average electrical energy use of 13,124 kWh for homes in the Northwest Region. (Baylon, 2012, Table 150). Assuming an average home size of 1,920 sf, the electrical energy use (EUI) is equivalent to 6.83 kWh/sf-year. This is equivalent to an average power draw of 1.5 kW.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 47%
Low and High Energy Savings: 30% to 60%
Energy Savings Reliability: 4 - Extensive Assessment
Assume that a CHP unit producing 1 kW of power is installed in each participating home. In addition to the electrical energy generation, waste heat can be recovered for space and water heating purposes. Assuming that the CHP unit is operated for 12 hours per day, the electrical generation is about 4,380 kWh annually. This generation alone is equivalent to about 33% of the typical home's annual electrical energy consumption. Heat in the reciprocating engine jacket water coolant accounts for up to 30% of the energy input to the engine (From ICF International, "Technology Characterization: Reciprocating Engines," prepared for the U.S. Environmental Protection Agency (EPA) in 2014). For small-scale units, this is about the same as the percentage of input energy that is converted into electrical energy. About 34% of the single family homes in the region have electrical space heat (Table 51) while about 55% of homes have electric water heating (Table 103, RBHS). The U.S. Department of Energy (USDOE) Building Technologies Program indicates that an electrical resistance water heater would require about 2,600 kWh/year. It will be assumed that recovered heat offsets the residential hot water heating requirements. The total savings from the CHP unit are thus 6,980 kWh annually, or about 47% of the residence's total electrical energy use.
Energy Use of Emerging Technology:
3.6 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:
Only the technical potential of those homes currently heated by electrical appliances can be counted. It is assumed that combined heat and power will get minimal penetration in the multifamily market in the foreseeable future. According to estimates in the Northwest Energy Efficiency Alliance's (NEEA's) 2011 Residential Building Stock Assessment (RBSA), 34.2% of single-family homes and 70.1% of manufactured homes in the Northwest are heated with electricity (Baylon, 2012). The simplifying assumption is made here that electrically-heated homes are the same average size as each category of home with all heating sources, so to get an estimate of square footage, multiply the total square footage of each type of home times the percentage of homes that are electrically heated in that category.
For CHP to be cost-effective, the electrically heated homes must have natural gas available as a source of fuel. It is not known what percentage of residences have access to natural gas, but where it is available, it is often selected for space and water heating due to cost considerations. The CHP is better suited for larger homes (i.e. >2,500 sf where thermal loads are higher). It will be assumed that 15% of the electrically heated homes have over 2,500 sf of floor area and have access to natural gas. The total residential potential is then reduced to 0.15 x 3,248,508,081 = 487,276,210 sf.
|Type of Home || No. of Homes || Avg. Size || Total s.f. || % Electrically Heated || s.f. Electrical |
| Single-Family || 4,023,937 || 2,006 || 8,072,017,622 || 34.2% || 2,760,630,027 |
| Manufactured Home || 543,730 || 1,280 || 695,974,400 || 70.1% || 487,878,054 |
| Total || 4,567,667 || 1,948 || 8,767,992,022 || || |
Regional Technical Potential:
1.56 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)
Currently no data available.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
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.