Conversion to gas? ? ?

[Paul M. Eldridge]

Hi Robert,

Much all of Nova Scotia is the same and in some areas you'd consider yourself damn lucky if you had more than two inches.

Cheers, Paul

[Paul M. Eldridge]

Hi Pete,

Thanks for the clarification. I hadn't heard of this technique before so I appreciate you taking the time to describe it to me.

From what I understand, the cost of a ground source heat pump is typically two to three times that of a conventional air source system so if, for argument sake, we peg the cost of our standard system at $7.5K the equivalent GSHP would be $15K or more. Obviously, the exact cost of either system would depend upon a host of factors, but for now I'm going to assume the premium runs in the range of $7,500.00.

As a quick, back-of-the-envelope exercise, an average new home with a space heating demand of 15,000 kWh/year, if equipped with an air-source heat pump (8.5 HSPF/Zone 4) would use roughly 6,000 kWh/year. That same home heated by a GSHP (seasonal COP of 3.75) might come in closer to 4,000 kWh/year. The difference of 2,000 kWh at $0.12 per kWh works out to be $240.00 a year; we might reasonably assume DHW and air conditioning savings kick in another $360.00, in which case our combined savings total $600.00/year -- on the other hand, an air source heat pump with a desuperheater might claw that back to less than $400.00. Nonetheless, if we assume an incremental savings of $600.00, the simple payback here is 12.5 years, with various cash discount rates and utility rate assumptions moving the exact position one or more years in either direction. If the breakeven point, as in this example, is more than ten years, it's fair to say your money would be better spent elsewhere; for a lot of consumers, even a five year breakeven point is a dicey proposition.

Again, these are rough numbers and we can fine-tune them further, but I wanted you to understand my base assumptions.

Cheers, Paul

[Pete C.]

Interesting. How do you figure that would work out in North Texas (north of Dallas) where there is a lot of A/C load in 100 degree weather and a surprising amount of heating demand in the winter as well? Another non monetary factor to consider is the lack of an outdoor unit with a somewhat noisy fan, and the need to clean it regularly of dirt, pollen, leaves, etc. This is of particular interest since I expect to replace the full HVAC here, probably next year. I also expect to be here quite a few years longer.

[Paul M. Eldridge]

Hi Pete,

I can explore this in more detail later on when time permits, if you so wish, but right now it's getting late and I'll soon have to call it a night.

Anyway, in terms of operating performance, SEER ratings are suppose to be reasonably representative of what we can be expect to encounter over the course of the entire cooling season. However, if it is helpful, EER is based on steady-state operation at a 95F ambient temperature (not far from the 100F mark you mention). To get a rough sense of how these two numbers compare, you can convert SEER to EER by multiplying the former by either 0.9 (relatively low humidity) or 0.8 (high humidity). So, if we assume you live in a hot and humid area, an ultra high efficiency heat pump with a 21 SEER rating would have an EER of 16.8 and a high efficiency model with an 18 SEER rating would have an EER of 14.4. To then convert EER to COP -- a more useful measure when comparing these products to GSHPs -- take this second number and divide it by 3.4. Thus, our 21 SEER unit would have a COP in the range of 4.9 (@ 95F) and the 18 SEER version would clock in at about 4.2. Again, this is a rough approximation, but the results seem to be more or less in line with what we could expect from a typical GSHP.

Your concerns related to noise are hard for me to address. The CAC in my Toronto home is a two-stage high efficiency model and on the low setting the outside compressor is surprisingly quiet (a light and not unobjectionable hum). I don't ever recall it kicking on high so I can't honestly tell you how loud it is when operating at full capacity. I don't believe I had any issues with dirt, leaves or pollen -- I may have washed down the outer cabinet with soap and water once or twice but that's basically it.

A GSHP may very well prove your best choice given your particular needs, utility costs, operating environment and so on -- I really can't say. But I wouldn't automatically rule out a high-efficiency air source heat pump without investigating this option further; these products have really come a long way in recent years. Whatever you ultimately decide, good luck!

Cheers, Paul