Air-source heat pumps at high altitides
gjmw
| Posted in Mechanicals on
I’m wondering how air source heat pumps measure up to conventional forced air heat from an ecological point of view at altitudes above 5,000 feet? I used to work for a company that built net zero homes in Northern New England, and heat pumps helped us.
How does the ecological impact of air source heat pumps compare to other forms of heat at altitudes above 5,000 feet? Do they still make sense to install at high altitudes (from an ecological perspective)?
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Replies
Micah,
It sounds like you are asking two questions:
1. How does altitude affect the performance of an air-source heat pump?
2. Which type of heating system is better from an environmental perspective: an air-source heat pump or a "conventional forced-air heating system"?
The answer to the first question is that air-source heat pump performance can be affected by altitude, and in some cases the equipment needs to be de-rated to account for altitude. For more information, see this Q&A thread: How much are mini-splits really affected by altitude?
The answer to the second question depends on what you mean by a "conventional forced-air heating system." For some people, that means an air-source heat pump from an American manufacturer, hooked up to forced-air ductwork. I would say there is no ecological difference between that type of system and ductless minsiplits.
For other people, a "conventional forced-air heating system" is one that includes a furnace fueled by natural gas or oil. If that's what you are thinking of, I would say that a system that uses electricity is preferable to one that burns fossil fuel, for several reasons:
1. Burning fossil fuel contributes to global climate change.
2. Electricity is more compatible with PV systems.
3. The electricity grid is getting cleaner every year, as we transition to an all-renewable future. Most green builders advocate in favor of all-electric homes.
Hi Martin,
Thanks for your response. I guess the gist of my question is: once the decrease in efficiency of air source heat pumps at altitude is accounted for, are they still better from an environmental perspective than a fossil fuel powered furnace? Also part of the equation is the fact that electricity in my region often comes from burning fossil fuels.
It sounds like your answer is yes, because grid powered electricity (even when produced from fossil fuels) is still cleaner than burning fossil fuels on site to power a furnace?...and it anticipates the move to renewables... Did I get that right?
Have a good day,
Micah,
Weighing environmental pluses and minuses involves judgment. It's silly for me to pretend that there is a single "green" solution to all dilemmas.
I guess it's fair to say that not building any new buildings is the best green approach. Every time we build a new building, we are doing environmental damage. So it's best not to build at all.
If we do build, our building should be as small as possible, and should be designed to use as little energy as possible (congruent with our simultaneous need not to overinvest in expensive energy-efficiency gadgets).
Good luck figuring it all out! When in doubt, rent an apartment in an older city, downtown, near a bus stop or a train station.