Global Warming Impacts of Ground-Source Heat Pumps 
Compared to Other Heating Cooling Systems

A background analysis for the Buildings Table of the National Climate Change Program
This report was prepared in 1999 for NRCan's Renewable & Electrical Energy Division, to support the extensive involvement of Bill Eggertson of EESC on the Buildings Table of the federal climate change program. The full report is available from NRCan in Ottawa.
 
 

Heat pumps can significantly reduce primary energy use for building heating and cooling. Heat pumps utilize renewable or solar energy stored in the ground near the surface (ground-source). The renewable component (66%) displaces the need for primary fuels which, when burned, produce greenhouse gases and contribute to global warming.

This analysis was undertaken on behalf of the Renewable & Electrical Energy Division to estimate the Total Equivalent Warming Impact (TEWI) of ground-source heat pumps compared to other heating and cooling systems in residential, commercial and institutional buildings. The modelling results show significant emission reductions in major cities in all regions of Canada. The impact of heating only is examined in residential buildings, whereas both heating and cooling impacts are examined in commercial and institutional buildings.

TEWI Analysis

TEWI analysis can determine the overall contribution to global warming from energy using equipment over its operating lifetime (20 years). The electrical energy required by the equipment can result in releases of CO₂and NO_x at the power plant. Fossil fuels burned for heating purposes release CO₂, CO and NO_x , which also contribute to global warming. Leakage of refrigerants, used in both chillers and heat pumps, contributes to global warming. The greenhouse gases released from fossil-fuel electricity production and combustion are referred to as the indirect TEWI effect; the leakage of refrigerants into the atmosphere is referred to as the direct effect, and the impact of leaked refrigerants is much greater than that of CO₂. 

The fuel used for electricity generation determines whether the electricity production results in large emissions of CO₂. In Canada, hydro-power plants produced 64% of the total electricity generated in 1996, 16% from nuclear, and 20% from fossil fuel combustion. The latter are large producers of CO₂, while the former produce none. The electricity generation mix varies widely across Canada. In BC and Quebec, 90% of the electricity is produced by hydro plants. In Ontario, over 50% of the power is produced in nuclear plants with the remainder split between fossil-fuel and hydro plants. In Alberta, Saskatchewan and Nova Scotia, over 80% of the power is produced in fossil-fuel plants. 

TEWI Analysis
Atmospheric emission and fossil-fuel electricity generation factors are from provincial utilities and Statistics Canada. Electric utility transmission and distribution losses are from the NEB. Emission factors for natural gas combustion and oil combustion are from NRCan. A natural gas transmission loss of 0.33% is assumed. Refrigerant charges (R-22), for calculating the direct TEWI effect, reflect those of currently available equipment. Refrigerant leakage rates are from Environment Canada's Expert Panel on Alternative Refrigerants.

Energy Modelling

The residential house model had 230 m²of floor area above grade, window area of 23 m² , insulation levels of R-20 in walls, R-30 in roof, basement wall insulation of R-10 applied to 0.6 m below grade. Windows were double-glazed. Energy consumption of the competing heating systems was determined using the HVAC Advisor computer program for Vancouver, Toronto, Montreal and Halifax. The ground-source heat pump was closed-loop and modelled using similar seasonal energy calculation procedures as those in HVAC Advisor for air-source heat pumps. 

The commercial / institutional model are a small multi-unit residential building and a primary school. The MURB is a 4-storey, 44-suite building with underground parking garage. The school is a 2-storey building with 4,260 m² of floor space. Total energy use was determined using DOE 2.1E energy analysis program. 
The energy efficiency characteristics of the model heating equipment, ground-source heat pump, chiller and boiler are summarized in Table 1. The residential equipment (with the exception of the oil furnace) is high efficiency. The commercial/institutional base case meets the requirements of 1997 MNECB. The ground-source heat pumps are high efficiency, available in the market place.

Table 1: Equipment Energy Efficiency Characteristics

Residential Heating Equipment Energy Efficiency Rating/Value

electric furnace AFUE ­ 100% 
oil furnace AFUE ­ 78% 
ground-source heat pump COP @ 0C ­ 3.3 
natural gas furnace AFUE ­ 90%

MURB

reciprocating chiller COP 3.8 ­ 
boiler ­ Ec 80% 
ground-source heat pumps: EER 15.5, COP 3.4

reciprocating chiller COP 4.2 ­ 
boiler ­ Ec 80% 
ground-source heat pumps: EER 15.5, COP 3.4

Results of TEWI Analysis

Residential Heating Systems (Table 2)

The ground-source heat pump has the lowest TEWI or total equivalent mass of CO₂ over the 20 year lifetime, in all the cities examined. The electric furnace has a lower TEWI than oil furnace and natural gas furnace in Vancouver, Toronto and Montreal, due to the relatively small fraction of fossil fuel electricity generation in these areas. In Halifax ,where over 80% of electricity production is from fossil fuel, the oil furnace has the second lowest TEWI. In Vancouver, the oil furnace, which meets the Canada minimum AFUE of 78%, will produce over 13 times the equivalent CO₂ emissions of the ground-source heat pump. In Toronto, this is reduced to six times. In Vancouver, the high efficiency natural gas furnace produces over eight times the lifetime greenhouse gas emissions of the high efficiency ground-source heat pump. In Toronto, this is reduced to 3.5 times. Only in Halifax, and other areas where significant electrical generation is by fossil-fuel plants, do conventional furnaces have comparable TEWIs to ground-source heat pumps.

Commercial/Institutional Buildings (Table 3)

The ground-source heat pump has the lowest total equivalent mass of CO₂ or TEWI impact, in both the MURB and primary school building, in all cities. The magnitude of the reduction depends on the base case system efficiency and the electrical generation mix, to a high of 77% in the primary school in Montreal. The direct TEWI effect due to an assumed higher refrigerant leakage rate, is higher for the GSHP packaged system than for the modern central reciprocating chillers in the base case. The direct effect varies from city to city due to variations in equipment size and hence the refrigerant charge.

Conclusions

Significant emission reductions are available through the application of ground-source heat pumps in both residential and commercial buildings. For the models studied here, residential fossil-fuel heating systems produced anywhere from 1.2 to 36 times the equivalent CO₂ emissions of ground-source heat pumps. In the two commercial/institutional cases examined, CO₂ emission reductions from 15% to 77% were achieved through the use of ground-source heat pumps.

Ground-source heat pump equipment is widely available throughout Canada. The equipment is competitive on a life-cycle cost basis with those systems examined here, particularly in those markets where air-conditioning is desired. There is unlikely to be a potentially larger mitigating effect on greenhouse gas emissions and the resulting global warming impact of buildings from any other current, market-available single technology, than from ground-source heat pumps.