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Estimating the savings on energy costs an air source heat pump will provide

Estimating the savings that you will receive by adding an air source heat pump to an existing furnace involves three factors:


1) A comparison of the heat pump’s efficiency to your furnace’s efficiency
2) A comparison of the price of electricity to the price of natural gas (assuming you have a gas furnace)
3) Estimating the percentage of your home’s heating requirements that will be provided by the heat pump



Part 1: Comparison of the heat pump’s efficiency to the furnace’s efficiency


COP (coefficient of performance) ratings are published for many heat pumps. These indicate the watt-hours of heat provided for each watt-hour of cooling, for a given temperature. For example, the Amana ASZC18, with an HSPF of 9.5 (for the 4 ton unit in high stage with appropriate indoor coil & furnace), achieves these COP’s at the following temperatures (see the datasheet for the complete table):

65F (18oC): 4.80
50F (10oC): 4.26
40F (4oC): 3.82
35F (2oC): 3.61


So a heat pump will provide efficiencies of between 361% and 480% (at temperatures below 25F/2oC, the furnace will usually be used). For this example, we will take the average of these two numbers, 420%, to estimate the average efficiency of the heat pump.


Part 2: A comparison of the price of electricity to the price of natural gas (assuming you have a gas furnace)


In BC, electricity is more expensive than natural gas for the amount of energy provided. Fortis BC (as of June 2012) charges $7.87/GJ of natural gas (including delivery costs & midstream charges).  BC Hydro currently charges a “tier 1” rate of 6.80 cents/kWh for the first 675 kWh’s each month and a “tier 2” rate of 10.19 cents for each additional kWh. Since there are 278 kWh in 1 GJ, BC Hydro is effectively charging a tier 1 rate of $18.89 per GJ of electricity and a tier 2 rate of $28.30 per GJ. So electricity is basically 2.4 times as expensive as natural gas under the tier 1 rate and 3.6 times as expensive under the tier 2 rate.



The heat pump averaging 420% will only use 23% as much energy as a 95% efficient furnace. But if the electricity it consumes is 3.6 times as expensive as the natural gas the furnace uses (BC Hydro tier 2 rate), the energy costs for the heat pump will be 17% lower (23% x 3.6 = 83%). But if the electricity is billed at the tier 1 rate (in a home with lower consumption), the energy costs for the heat pump will be 45% lower (23% x 2.4 = 55%).



The above calculations are for a fairly new and efficient furnace. If you instead consider a pre-1995 65% efficient furnace, the heat pump will only use 15% as much energy. The estimated energy savings will then be 46% if electricity is billed at the tier 2 rate and 64% if billed under the tier 1 rate.

 

 

65% Eff. Furnace

80% Eff. Furnace

90% Eff. Furnace

95% Eff. Furnace

Tier 1 electricity

64%

54%

50%

45%

Tier 2 electricity

46%

32%

24%

17%

Estimated savings on heating energy costs after adding a heat pump (with an average COP of 4.2)

 



Part 3: Estimating the percentage of your home’s heating that will be provided by the heat pump


From September 2011 to March 2012, Vancouver only had 37 days with an average temperature below 3oC and 7 days with an average temperature below 0oC, according to the National Climate Data and Information Archive. This should mean that, for most homes, over 80% of the heating requirements can be provided by an air source heat pump (although this will vary depending on many factors such as the size of the heat pump).

 

 

65% Eff. Furnace

80% Eff. Furnace

90% Eff. Furnace

95% Eff. Furnace

Tier 1 electricity

51%

43%

40%

36%

Tier 2 electricity

37%

26%

19%

14%

Estimated savings on heating energy costs after adding a heat pump (with an average COP of 4.2), after accounting for the furnace still providing 20% of the heat (savings reduced by 20% from previous chart)

 


Conclusion


Basically, even in the circumstances that will result in the lowest savings (a high efficiency furnace, low natural gas prices, high electricity prices) an air source heat pump will still have slightly lower energy costs than a furnace.



If the price of gas rises again, then air source heat pumps will again deliver huge energy savings. But with the current low price of natural gas, heat pumps usually will not have short payback periods (less than 7 years or so), especially once you consider potentially higher maintenance costs. Still, heat pumps offer lower utility costs, provide air conditioning, and can reduce your carbon footprint substantially.

 

A note on the HSPF ratings that are provided for all air source heat pumps:


The HSPF (Heating Seasonal Performance Factor) rating is based on the efficiency a heat pump will ac
hieve when heating a typical home during a typical year for a given region (the ratings for Region IV, which includes Vancouver, are usually listed). The better non-inverter heat pumps now achieve HSPFs of about 9.5. The HSPF rating refers to the average number of Btu’s of heat that will be produced for each watt-hour of electricity consumed. Energy wise, 1 watt-hour is the equivalent of 3.41 Btu of heat, so a heat pump with an HSPF of 9.5 could be considered to be 279% efficient (9.5/3.41). However, the HSPF also assumes that an electric air handler will provide the back up heat when the outdoor temperature is too cold for the heat pump to be used. Since an air handler will be more expensive to operate than a typical furnace, the HSPF rating will likely underestimate savings.

A note on the expected accuracy of these estimates:


The efficiency ratings for both heat pumps and furnaces are based on laboratory tests and will differ from the efficiency in real world applications. Thus, these estimates should be considered rough approximations.

 

Learn more about the other benefits of a heat pump on our heat pumps page.


Call 604 GOOD GUY (604 466 3489) to schedule a free in-home consultation and quotation on a heat pump. Or use our online form.


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