Post 2031: Both of my heat pumps have died? This should be interesting.

Posted on October 13, 2024

 

 

My house is heated and cooled by two ground-source heat pumps, installed by the previous owner almost exactly 20 years ago.

Well, “was heated and cooled”.  One died last spring.  The other has one foot in the grave, with its most recent repair involving some burned wiring (never a good sign).  Both heat pumps need to be replaced. 

No-brainer, right? Just replace them.

Well …

The only firm in my area that specializes in ground-source heat pumps quoted me a price of $50,000 to replace my two three-ton (ground-source) heat pumps.  That’s for the basic model.  Bells, whistles, and line sets extra.  I’m guessing the final cost would end up around $60K.

 

At this point, the only thing I know for sure is that no matter what, this home repair is going to be about like buying a new car.  Or two.

Minus the fun.

Follow along for the next several posts, as I get a handle on what to do next.

Am I a heat-pump heretic?

I drive an EV.  Cripes, it’s a made-in-USA Chevy EV, for that matter.

I re-calculate my family’s carbon footprint every couple of years.

And I bought my house specifically because it had efficient ground-source heat pumps.

But the world continues to change.  And I’m not sure I’m going to be replacing those with new ground-source heat pumps.

And the fact that I would consider not doing that makes me something of a heretic.  But I’m still in the process of gathering my facts.

  1. Twenty years ago, ground-source was the undisputed king of heat pumps.
  2. In part, that’s because air source heat pumps of the time weren’t very good.
    1. They worked inefficiently when it was cold out.  To the point of essentially not working.  That caused use of “secondary heating”, meaning, typically expensive and inefficient resistance electric heating.  In winter, your fancy heat pump spent too much time operating as more-or-less a big dumb electric space heater.
    2. And they weren’t any great shakes, efficiency-wise, the rest of the time.
    3. Plus, they just kind of generally sucked.  Comfort-wise.  In the winter, they always seemed to blow air that was, upon careful measurement, slightly warmer than the existing room air.  Or, at least, that’s how I recall my Maryland apartment of the mid-1980s.
    4. Basically, they were air conditioners that, in this climate (Virginia), could also put out some heat, for some of the winter.
  3. My impression is that this changed about ten years ago.  At some point, cutting-edge air source heat pumps appeared to be — by my calculation — at least as efficient as my 2004-vintage ground source heat pumps.
  4. That’s because air-source technology improved rapidly, while the technology of ground-source units … lagged?
    1. Part of the improvement was in finding a way for air source heat pumps to function well even at low outdoor temperatures.
    2. That went hand-in-hand with greater efficiency of operation.  E.g., modern air-source units might now have variable-speed compressors, fans, and so on.
    3. But not much seems to have happened to ground source heat pumps.
    4. The slower rate of improvement in ground source heat pumps is a side-effect of the vastly lower volume of ground-source (about 0.5% of the home market) compared to air-source (the other 99.5%).
  5. As a result, ground-source heat pumps are no longer a slam-dunk winner, compared to traditional air-source heat pumps.

    1. As a matter of basic physics, they should be.
    2. But because they seem to be behind the curve in efficiency improvements, they aren’t.
    3. The upshot is kind of a temporary tie:  The rapid adoption of more efficient technology in the air-source sector has offset (or nearly offset) the inherent physics-based advantages of ground-source heat pumps.  For now.
  6. There is no point number 6.
  7. But the tax laws still grossly favor ground-source heat pumps over air-source.  And the subsidies are large.
    1. For ground source, the Feds pick up 30% of the installed cost, no limits.
    2. For air source, if it meets certain efficiency standards, the Feds pick up a maximum of $2000 (or 30% of the installed cost, whichever is less).
    3. And Virginia offers an incentive system for ground-source that is beyond weird, and must be described in a separate posting.  At first blush it appears ludicrously generous toward ground-source units.
    4. Separately, I’m not sure they were thinking about replacements of worn-out old systems when they wrote the law.  Effectively, what I’m doing is repairing my existing system, by replacing the worn-out heat pumps. But, legally, that’s treated identically to putting in a brand-new ground source heat pump system.
  8. So, something is not right here.
    1. Is the law outdated, and out-of-step with the current state of technology?
    2. Or is the law a closet buy-American plan, as these ground-source units seem to be U.S.-made?
    3. Or am I dead wrong about the near-equivalence of air-source versus ground-source efficiency in the modern world?
    4. Or, some thing even weirder — geothermal versus ground source discussion to be added at some point.
  9. Curveball:  My first floor would be ideal for a couple of “ductless mini-split” systems.  These are little air-source heat pumps, but instead of being designed to hook up to your ductwork, they simply blow air around like a room air conditioner.  You pass the refrigerant pipe and condensate drain through an exterior wall, between the inside air-distribution cabinet, to the outside compressor.
  10. So, why not replace one of the dead ground source heat pumps with two mini-split air source heat pumps, half the size.
    1. Near as I can tell, I’d pay only a modest or no efficiency penalty for doing that.
    2. And it looks like it would be quite a bit less expensive, even accounting for likely shorter equipment life of an air-source system.
    3. Plus, we’d possibly have a warm kitchen for the first time since we moved here, because we could bypass our near-useless 1959 first-floor ductwork.
    4. Plus, it’s lower risk — more like an appliance, and less like a fixture in the house.  If one of those dies, I can just toss it and more-or-less just plug in a new one.  Not quite as convenient as a fridge, but not hugely different.
  11. But … but … but … the very thought of replacing a ground-source heat pump with an air-source heat pump is … heresy.  Particularly given that the actual “ground” portion of the ground-source system — the mile of plastic “slinky” pipe buried in my back yard — still functions perfectly.

Conclusion

That’s as far as I can take it in this first post.  I need to pin down some facts to go any further.

I bought this house in large part because it had an efficient ground-source heat pump.

But the world has changed since I bought it.

The next post takes the two real-world heat pumps — one a ductless mini-split air source heat pump, one the ground-source heat pump for which I have been quoted an installed price — and tries to get an apples-to-apples comparison between them, in terms of efficiency.

That turns out to be stupidly hard to do.

That’ll be the next post:  SEER, SEER2, EER, EER2, COP, HSDF and all the rest of that alphabet soup.  And how on earth they measure that, for ground-source heat pumps.