Heat pump disappointment for climate-minded Massachusetts state senator
willbrownsberger.comIt's good to see a politician actually doing their own analysis rather than just following every fad. It's a characteristic that is sorely lacking from the US political class.
The US Political Class is made up of Gullible people unable to do their own research because that is what the system has incentivized electing
People with intelligence, principles, and convictions rarely last long in politics;
People lacking those skills but the ability to charismatically reiterate the talking points of politically connected charities, action groups or lobbiest are well sought after....
A more optimistic interpretation of "The US Political Class is made up of Gullible people unable to do their own research because that is what the system has incentivized electing" would be that the US political class can't possibly do their own research on every topic that they have to govern and instead have to rely on external experts. Not arguing that it ends up being those with the most money being the loudest, but it makes sense that you'd want to use the research of others for your own decision making if you're not an expert and have access to experts.
They're not "gullible" -- they exist to flog the views of those who elected them; that's their job. They exist to be a sock puppet for their voters.
Think tanks exist to come up with policy prescriptions. There are just so many topics, internationally, locally, nationally, that no one can be a deep-dive expert unless they focus specifically on it.
I would agree with you if that person would have mentioned research paper and not just some very weak anecdotal evidence.
I find it very weird that their heat pump leaked and the efficiency is only at 150%.
It's not clear at all if this is an crazy outlier or reality.
IF this is not just an outlier than the next proper step from him would be to get the ball rolling with the right people to investigate the status quiet and fixing it.
Heat Pump efficiency is inversely linked to outside air temp, the colder it is outside the less efficient the heat pump is as there is less heat energy to extract from the outside to "pump" into the inside...
Fixing is called physics... I am not sure magic words on a page (regulation) will "fix" physics....
It's really difficult to understand what is going on with this politician's heat pump though because we are lacking a lot of basic information. A high quality minisplit system should top out at a COP of over 3.5 and be above 2 down to single digit F temperatures. E.g., https://www.mitsubishitechinfo.ca/sites/default/files/SB_PVA... has a COP of 2.17 at 5F. It seems like there is more to the story. A small duct/high velocity system could perform that poorly, but without the details it's just hard to tell. Most folks with normal ducting or ductless heat pump systems should realize much better efficiency than this guy is getting.
Well looking up the specs for an Amana Budget system [1] that is more typical for what you would find in American home (mini Splits are rare here, and normally installed in Garages and Shops, not primary residences ) 1.5 Ton unit COP drops to 1.4 @ -5 and only matches the efficiency of the minisplit you linked @ 10 degrees
if I look at the high end an Amana System[2] and 2 Ton unit (which is more common size in the US) COP drops to 1.7 @ -5 and drops to about 2 at single digits.
[1] https://www.amana-hac.com/pdfviewer.aspx?pdfurl=docs/default...
[2]https://www.amana-hac.com/pdfviewer.aspx?pdfurl=docs/default...
Elsewhere he says that his heat pumps are two Daikin RJQ18TAVJUA:https://ashp.neep.org/#!/product/56878/7/25000///0.
Much of the other information is probably available elsewhere on his site: https://willbrownsberger.com/heat-pumps/
As I mention in another comment, I think the base of the problem is that the heat pumps he has installed are simply inappropriate for his climate.
> I think the base of the problem is that the heat pumps he has installed are simply inappropriate for his climate.
The question is whether there is such a thing as a heat pump that's appropriate for use in the Northeastern US. It seems unlikely to me that someone with this person's level of engagement would have stupidly chosen to install the wrong kind of heat pump or chosen an installer incapable of recommending the best options.
I live in New York State and the government is nearing the point of banning gas installations in new construction here. I have yet to see any real cost benefit analysis for such a policy in a state with such cold winters.
I agree it's still a somewhat open question, but I think the data is that Massachusetts is probably on the side where it can make sense with the right equipment. Here's a real world analysis of a heat pump in Connecticut that averaged an full heating season COP of about 3.0: https://www.nrel.gov/docs/fy13osti/56393.pdf
I disagree that he's unlikely to have chosen a bad installer. They seem to have installed a non-cold-climate heat pump in Massachusetts. If that's true, I think it's strong evidence that they were not competent and should not have been trusted. I guess one could argue that this was a low probability choice, but I think it's as likely there were simply no more competent installers available in his area.
fraud on the part of the manufacturer is a distinct possibility with that kind of discrepancy also
Brownsberger is my state senator and he's actually pretty great, he works on things his constituents care about and I've seen him on public transit a number of times.
My only real critique of him is that he had too much faith in the MBTA getting battery electric busses up and running when voting to get rid of our trolleybus system (MBTA 71 and 73).
Anytime you have a technology that is marketed ubiquitously as if it's a silver bullet solution, you are going to have disappointed users and implementations that under deliver.
Of course it's extremely important to switch people to electrified heating systems, regardless of their efficiency. However it's a little disingenuous to pretend there is nothing but upside here. The upside is for humanity as a whole; for individuals there may be very little noticable changes or improvements, and the systems may be worse than what they are used to.
>> Of course it's extremely important to switch people to electrified heating systems, regardless of their efficiency.
You could use a gas fired heat pump. It won't work as an air conditioner, but it won't stress the grid and could even work when the power goes out.
you are better of adding with a gas plant to the grid, which can be up to 84% efficient (if you reuse the heat generated by the turbine as well)
And even if you don't, a 60% efficient gas turbine at the power-plant, paired with a 3+ COP heat pump in the home will be 2x more efficient than burning gas directly in the home.
Using gas in an adsorption heat-pump is quite inefficient and unlikely to break even economically. Perhaps a gas turbine home boiler could be produced, that combines a mechanical heat-pump with a high efficiency combined cycle turbine; alas, they do not exist and would be very expensive. It's a startup idea.
A home gas furnace can easily surpass 90% efficiency. Turning the gas into electricity and then including the transmission losses to the home is going to be way below 84% efficiency. Plus reusing the heat produced at the power plant is much more difficult than reusing the heat produced in the home, when the purpose is heating the home in the first place.
Up to 64% as stated in the article. The 84% efficiency statement is in reference to the theoretical efficiency of a Carnot cycle.
64% for the turbine only
No. Definitely not.
>and could even work when the power goes out.
AFAIK gas furnaces still need electricity for the fans to work. When you have no electricity you at best have a glorified fireplace. It's probably going to be a worse than a regular fireplace because it's not designed to output heat to its surroundings.
The fan of a furnace takes little power. It can be run off of a small generator, which ~every homeowner in New England has.
A heat pump cannot run off a small generator.
Two notes: in a modern insulated home in not so cold climate 1kW absorbed is enough to heat a home with -20℃ outside, with is still far more than a simple fan but a power level a classic small generator can provide. The second note is that if you get gas from pipes the supplier need electricity to pump it, so it might have autonomous power or not, you can't be sure.
As a safeguard I prefer a classic wood burning stove, witch is far from being comfy but works alone, reliably and I can stock enough woods or emergency source it almost anywhere...
Living in the French Alps I do not know much about New England homes (insulation, ventilation, power system, ...) but IME gas heating systems are in the mean LESS reliable than heat pumps and electricity + wood is the combo to be comfy normally and backed up in case of trouble.
Yeah I totally agree. Heat pump with a wood stove / furnace as a second heat source is the way to go.
It's not unheard of to go multiple days without electricity after a bad snow storm, so I would never trust a heat pump alone. When you need them the most, they are the least efficient and reliable. And I want to have a fireplace anyway, so it makes sense to make it functional.
> It can be run off of a small generator, which ~every homeowner in New England has.
This is absolutely not true. I actually don't know anyone who lives in an urban area in New England that has a generator. And I know some who live in fairly rural Maine that don't have one.
Generators are not ubiquitous, or even common, in New England.
a (quasi) silver bullet solution, can have legitimate (individual) down sides
> I do not fault the particular pump that we bought or our installers who were careful and professional. Apparently, however, we lack good rules of thumb to predict how a pump will perform in a particular installation.
A 278% estimation turning out as 150% real world performance, certainly was not done very carefully.
His efficiency data is tarnished by the leak. It was doing its best, but it was leaking, so it probably had to work harder to get the proper temperature. Also, he's comparing year over year - years have differences in weather. He's comparing one year's gas furnace use to 9 years of heat pump use - this is not a great comparison. Also, if he'd have had solar, or some other source of electricity, that was cleaner, say nuclear or solar or wind, it would be a lot less.
No, it works exactly like solar does. The companies say one thing, but reality doesn't match up. It doesn't matter how careful an installation is.
Why not?
The real heating demand can be observed up front and with the typical (or even exact) weather you can easily determine the efficiency of the heat pump.
Yeah expect some inaccuracies, but not this huge
My weather person can't even predict what Thursday is going to do. You want accurate predictions for all of winter? That's why I mentioned solar. It's the same, but with sunlight.
no predictions necessary, just check out the data from last year
Why do you think the manufacturers mislabeled efficiency has any relevance to how the installation team performed?
I would assume the team knows the products they are installing
Bad assumption. It’s like expecting framers to know the ins and outs of LVL production.
They’re there to put widget A in widget B, according to the instructions.
That's a fairly inappropriate comparison in level of expertise necessary to design a system: LVL beams are picked by structural engineers, not by framers who generally install them where they're needed, based on a structural design which they have no say in because load calculations aren't a framer's job.
HVAC installers are not merely system assembly specialists, they're system design specialists as well in nearly all cases. Or at the very least they outsource HVAC system design to experts who are familiar with required air flow, static pressure, air changes, condensation formation and evacuation, and yes of course whether the system is appropriate for cold climates (cold climate heat pumps are notably different from temperate or hot climate ones: coils are larger to capture more heat from the air outside temperatures are very low); they have different refrigerant systems; and way more insulation to prevent the cold affecting operation; some even incorporate resistive heating elements... or a gas furnace in cases where their efficiency would drop below an acceptable threshold.
One of the biggest and most important part of an HVAC system design is sizing for climate and dwelling. It should be extremely suspicious to any installer that their design system efficiency would be so much higher than the real world system performs.
I'd be shocked if professional HVAC installers couldn't spit out several reasons why the system might be performing so poorly just by reading this blog post. Notably the absurd assertion that the installers were professionals despite wildly overpromising and underdelivering. Some contractors acting professionally doesn't make them professionals.
As others point out in this thread, implementing a system that meets the stated design goals roughly on target is what a professional does. I've seen some absurd lambasting of PV solar installs as an example of empty promises. Again, those are tell-tale signs of deficiencies, not an indictment of the underlying technology.
Which is the most irresponsible part of this senator's post. Given your post and prominence, the least you could do before publishing something like this is check your basic assumptions: that the installer did a fine job.
As someone who recently had a heat pump installed, your expectations for minimum wage workers is rather unrealistic. We asked for one, they estimated the cost and installed it, and we paid the bill.
It was their second installation, ever. Red state with lots of gas installations and all that.
The onus of understanding that it wouldn’t work under a certain temperature, and would get lower in efficiency the lower the temperature, was on me.
It wasn’t that hard to understand, either.
The real world performance is with one of the units malfunctioning for weeks.
This is why I couple my heat pump operation to solar output from my panels. Any time I can fully self power it is a 100% win. During the darkest and coldest months however, the existing gas boiler takes the lead.
My heat pump is 5 years old and has never leaked refrigerant. I also collect the condensate for the gardens.
>> During the darkest and coldest months however...
How cold are the coldest months?
http://www.worldclimate.com/climate/us/massachusetts/framing...
The averages do not illustrate the extremes very well, we see many days where the nighttime temperatures never rise above 0F.
It seems ridiculous that refrigerator leaks are not "an uncommon occurrence". Does anyone have any insight into why this would be?
This is a great question. Data from this website[0] suggests heat pumps leak at 6%/year vs. traditional condensing units which leak on average at 10%/year, so it seems they are still an improvement over traditional ACs. One technician's experience[1] points to the steel accumulator rusting being the primary cause of heat pump leakage. There was a big 2014 study in the UK[2] on heat pump leakage, but no causes were identified, due to poor data collection.
[0] https://support.accuvio.com/support/solutions/articles/40000...
[1] https://highperformancehvac.com/heat-pump-leaking-refrigeran...
[2] https://assets.publishing.service.gov.uk/government/uploads/...
Because flare fittings are a concession to make install cheaper, not better. R410a and other similar refrigerants are very high pressure, and the fittings undergo significant thermal cycles. Flared copper tube is a bad design choice. IMO, going back to brazed tubing connections is the most rational choice.
brazed tubes can leak as well. I had that happen in my last house. Little leaks are hard to find, the first time I had the system refilled the tech couldn't find anything and put some sealer in. The next time the tech did the same and was disconnecting the fill lines when he saw a dark spot, then he emptied the lines and did the proper fix.
Sure, anything can leak. Brazed fittings when executed properly and tested are much less likely to _start leaking_. the issue is that the flares have a tendency to work harden during the constant vibration and thermal cycling and eventually give up.
FWIW, I just had a heat pump installed, and the installer brazed all copper fittings. Are flared fittings often used for these installs?
Most mini splits use flairs, and in the context of heat pumps in the US, I see Minisplits most commonly discussed. The whole house condensers still use brazed connections.
If you have a badly soldered (brazed, welded, or other way to join pipes) joint it will still hold pressure for a month or two. Then mechanical vibration will slowly degrade the joint and eventually metallic fatigue will cause a small break and then you get a leak.
Note that most of these leaks are caused by installation. In the factory they have things they can do for quality control to make such things not an issue, but the refrigerant needs to get from inside each house to the outside and that means custom install which makes quality control harder.
Worse, it is hard to find leaks. Often the pipes are buried in walls and so all the tech can do is put some sealer in and hope that fixes the issue. There is the ability to put some leak detector in the lines, but then you need to spend a lot of labor and still not guarantee.
I don't know what can be done about it, but I know it is a real problem.
Leaks are common with quick-install couplings and shoddy soldering. They seem to be more prevalent in the US, because qualification requirements for the installation of A/C and heatpumps are low to nonexistent, and anyone can just visit the DIY store and get refrigerant refills. So a leak isn't much of a problem beyond getting a cheap refill for most people, so craftsmen don't prioritize leakproofness.
I have a 12,000 sqft building in the northwest corner of Massachusetts. Really well insulated and heated entirely with heat pumps. I have a large solar array to offset the costs. I ending up paying around $1.50 this year for all the electricity. If I factor in my SRECs sales it drops to around $.75. Last august the Governor signed new legislation that increased the the price utilities pay for the KWhs I produce so I expect another reduction in cost. The biggest problem I have is that 5 years ago all the HVAC installers claimed one couldn't use a heat pump in our area. Now we need many more installers than are available. Our local vocational school just added an HVAC heat pump program for the build back better funds.
> The biggest problem I have is that 5 years ago all the HVAC installers claimed one couldn't use a heat pump in our area. Now we need many more installers than are available.
Heat pump technology has been advancing rapidly particularly in cold weather performance. I don't know if that was entirely accurate 5 years ago. But it was certainly MORE accurate then particularly for NW Massachusetts.
And we certainly do have a lack of good installers right now, unfortunately.
I got one installed at the time they existed but nobody had seen one work so it was easier to claim it is impossible. What has really advanced is the importation of heat pumps.
Daikin makes an Altherma line that is excellent an was removed from the US market a few years ago. Not becuase it doesn't work but becuase the US believe it doesn't work. I often toy with the idea of buying one in Canada. I need a Harry Tuttle of heating engineers.
If I were building new in the north, ground-loop heat pumps make more sense, less maintenance, less trying to eek out a temperature difference. You will likely already have the equipment on-site for grading and foundation work. No need to remove material permanently for it…
I’d love to hear experiences on ground source installs in suburbs. I’d love to do one but feel like I’d be forced into a vertical well which I’ve always heard is an outrageous cost. I’d love to be wrong.
I'm also wondering about the cost of maintenance and repair (say, in case of an underground refrigerant leak). I too would love to be wrong - it'd be a decent solution for a cold Albertan winter. It doesn't matter that the air is -40 if you're below the frost line.
I have two self-installed ground source heatpump units (6 tons total) in operation since summer of 2016 with no maintenance except for the loop pump. I was using two very old second-hand pumps until last summer (one for each unit), when one impeller completely disintegrated. I took the opportunity to reconfigure the plumbing and wiring a little bit to use only one pump (more modern, theoretically better fit for my system), and it has been smooth sailing since then. We'll see how long the new pump lasts I guess.
As for loop installation, I have a few acres and dug a ditch with my dad's backhoe. Most homes around here don't even have room for a septic system, much less a horizontal ground loop. I can't speak to the cost of a vertical system, but I think it would also affect the specs of the loop pump, and not in a good way. Check for tax-incentives as well: I got a 40% tax credit on the units themselves when I bought them.
I have to edit to address the underground refrigerant leak: I haven't had to deal with this. I can only say that it would not be a fun time. I think in a properly installed and tested system, it shouldn't really happen outside of freak seismic events though, at least within a human lifetime.
How deep are your lines buried? Did you need to be concerned about the frost line?
My ditch was 8 ft. which I believe would be considered overkill. I'm also not worried about freezing at all (GA, USA). My system does more work in the summer than the winter.
OP fails to mention total cost of producing the new heat pump and opportunity cost of disposal of the old heat unit.
Brownberger seems to miss the key fact that you can't run a gas heating system on renewable energy.
Just as in switching to an EV isn't going to make things significantly better, switching your heating to heat pump isn't either:
Some basic tips from a fellow Bay Stater:
1. Any new or replacement mechanicals should be use heat pumps (water heater too)
2. Make sure your house is well-insulated to get the best bang for the buck
3. The grid has the ability to use greener energy as time goes on, and you can also opt in to renewable suppliers (in MA, at least)
4. Add a solar array and with net metering it becomes a no brainer.
> Brownberger seems to miss the key fact that you can't run a gas heating system on renewable energy.
Of course you can. You can use nat-gas-like gas mixtures from decomposition of different kinds of waste, e.g. biomethane and the like. You can also use hydrogen (within limits) and methane produced from green hydrogen (though usually inefficiently).
Is net metering available anywhere at all? Where I am it's long gone, and I hear in some areas they charge you to use your excess energy.
Net metering is still very much available in MA.
> if ... and your electric company allows it
So, do electric companies allow it?
> Brownberger seems to miss the key fact that you can't run a gas heating system on renewable energy.
just a small nit pick:
In theory you can produce methane from electricity, so it is possible. However the efficiencies are abysmal, which makes this almost always a very bad solution.
I wonder if we will ever see them switch to R-1234YF refrigerant. "While R-134a has a Global Warming Potential of 1300, R-1234yf’s GWP is less than 1." The only issue is the higher pressures and the fact that it's somewhat flammable might be why.
I will say, my heat pump dryer, while it has removed some buttons from shirts, has exceeded my expectations on energy usage. It's night and day compared to my toaster I had before.
And possibly this senator got a bad heat pump setup. Sample size of one although the leaking being common is not good.
I'm not sure if you will ever see that, the EU is currently trying to band all flourinated hydrocarbons, right in the middle of the 'we all need a heatpump' run. The only "viable" refrigerants after that will be CO_2, propane and ammonia. The "viable" is in scare-quotes because all of them are kind of nasty, CO_2 and ammonia are quite poisonous, CO_2 is inefficient or unusable for the temperature range in question, ammonia is very very corrosive and propane is flammable and explosive. Maybe the US will do the sensible thing and wait it out, meanwhile buying up all the cheap, working heatpumps with traditional refrigerants.
Is propane that bad? We have propane plumbed throughout houses everywhere here in the us, and while accidents happen they are extremely rare.
I would think that with a closed loop system the risk of a serious problem would be quite low.
The pressure is higher in A/C and heat pumps, and you have liquid propane in half of the system. A leak there will quickly create a huge volume of flammable propane-air-mixture at room pressure. The usual plumbing for heating and cooking is at a very low (over-)pressure, 100mbar or something, and your distribution network in town is typically at 1bar. A leak there is less bad and will take some time to fill up space with enough flammable propane-air-mixture to be dangerous, enough time to maybe sound an alarm and evacuate. Generally, a basement full will obliterate the occasional building in any case.
The new, (bio-)propane refigerated ones (R290) are pretty good and work well with the radiators most Europeans have at home. They are reliably capable of emitting up to 75C outlet water. At the moment they are approx. 1.5-2x more expensive, I hope that will come down somewhat. I really hope after a few years a good heatpump will reach cost parity with a good boiler (installation that is).
In your experience, does your heat pump dryer actually dry in a similar amount of time to a conventional electric dryer?
Nope, the toaster had a full load done in like an hour. The heat pump is like 3 hours. But the difference is the heat pump doesn't absolutely destroy my clothes. I'm noticing how much longer my clothes are lasting since switching. It's also so much quieter than the electric.
If you are the type of person who goes "oh crap I need to wash every piece of clothing RIGHT NOW" then heat pump isn't for you because of the time penalty.
Specifically, what the heat pump dryer is doing is basically pulling air through the clothing which evaporates some water from the clothes into the air, then cooling the air, which causes water to condense, removing the condensed water and warming the air back up to send through the clothes again. The effect is much closer to the clothes hanging from a line in a garden on a perfect drying day, except it's inside a box.
Whereas the other way to do this is just cook the clothes and the water evaporates, then you dump the warm moist air either outside or into a separate dehumidifier which throws much of the energy away. As you observed this is faster, but most people don't need faster if it's unattended. My dishwasher is slower than washing dishes by hand, but I don't need to sit there watching while it does it so who cares?
My heat pump drier dries a full load (8 kg) of cotton in about 4 hours. My only other experience was a huge, old unit when I lived in North America and I don't really remember if it was faster, but it absolutely destroyed any piece of cloth that wasn't resistant enough, especially anything with elastics.
My current one is as gentle as air drying, no destruction at all.
I have installed condensate dryers which are actually more efficient than heat pump dryers but take a couple of hours to dry. They don't need to be vented to the outside.
My heat pump dryer doesn't vent and captures the water to a tank or pumps it down the drain.
I think too many do not understand one point of the Green New Deal, perhaps because that point is NOT advertised: convergence toward electricity it's not different than convergence toward IP, it means choosing a tech we need anyway while not the cheapest and use it for almost anything cutting much costs.
For instance a heat pump have much less raw materials and need far less high costs alloys than a gas heating system, essentially is cheaper to be produced, and if we can stay on electricity only we can spare the maintenance and expansion costs of gas/oil/* distribution networks.
Try to compare classical mechanical clocks vs modern electronic ones: the mechanical one it's far more costly per single unit, the electronic one cost next to nothing per single unit. For EVs it's not different: they have much less parts, less special alloys, less precision needed to produce them.
Heat pumps and EVs have both evolution margins, while classic ICEs and gas heating systems have already reached a sort of evolution plateau.
Those are the reasons of the Green New Deal: ecology is advertised as the only reason, in reality is a MARGINAL reason, the main reason is reduce much the demand of raw materials (once the transition will be done, of course) and lower much overall production costs. I imaging such reasons are not advertised because most of the benefit will go to those how steer the transition, not to those who pay it. But that's is and understand it and it's need means also steer the actual transition in a way more interesting to the people than a very small cohort of cleptocrats.
> I do not fault the particular pump that we bought or our installers who were careful and professional.
I feel like the author may be letting the installers off too easily here. It seems like there are two main possibilities: either no one understands how heat pumps actually work in the real world and none of them meet their claimed efficiencies (possible, but in my estimation not that likely) or the heat pumps he has installed are unsuited for their purpose (or badly installed). I'm inclined to suspect that he was sold the wrong heat pumps.
Confirming this suspicion, in an earlier post (https://willbrownsberger.com/our-heat-pump-experience/#comme...) he gives the specs for his heat pumps. I don't know this particular model, but a commenter after him claims they are not the sort of "Cold Climate Heat Pumps" that would be appropriate for Massachusetts. Since this matches the symptoms (adequate heat production but low efficiency) I'm guessing this is the real issue here.
I think heat pumps are a great technology, but worry there is going to be a backlash against them unless we can rein in the hype. And something is has gone really wrong if local installers can't be trusted to install a heat pump that is appropriate for the climate they are being installed in. Maybe the best thing he can do as a Massachusetts state senator is to enact more stringent laws preventing the installation of non-cold-climate heat pumps in Massachusetts so others don't suffer the disappointment that he did!
One thing I am learning in doing research for local installers and HVAC companies is that you can't really trust any installer to do it right. Even the highest reviewed company will have tons of monthly reviews about wrongly installed equipment or bad advice to customers.
Like buying any major appliance, unless you shell out a commercial fee for a commercial product and contract, you're just gonna be rolling the dice. You can do it yourself but the heat pump unit itself may still vary dramatically from sales specs.
I intuited this as well, which is why I stayed with gas heat.
These days I'm even wondering if wood heat with a high efficiency furnace makes sense. There are so many dead trees around me. The carbon is going to go back either way. In the case of decomposition, there may be other negative effects of leaving it on the ground compared to burning it.
I haven't given much thought to a way to capture the heat in a way that can be used later. Ideally I can build some giant container of sand with some cinderblock, run some copper through the sand, and heat both using the wood being burned. Then, I could pump water through the copper which is being passively heated from the sand into my existing hot water baseboard, but it's unlikely to be hot enough - oh well.
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I actually looked at some old quotes I found for mini split installs before and after the tax credits Massachusetts introduced and *big shock*, the price of the installs increased about 90% of the tax credit.
If you have hydronic heating anyways then why not get a wood fired boiler? They're extremely common where I am. Why would you need to store the heat? A wood fire isn't instant on but it doesn't take that long either plus you get the heat from the stove itself well before the baseboards heat up.
I have a pretty high efficiency tankless boiler so it would be expensive and wasteful to switch at this point. It is possible to buy a wood fired boiler and hook it up to the house to supplement the tankless but I'm skeptical that makes financial sense.
I'm a bit confused since I thought you were talking about hooking up a wood fired furnace of some type. Putting a solid fuel boiler in line with an existing system is pretty common and doesn't have any impact on the system as a whole efficiency wise except for a tiny bit of heat lost to the length of pipe in the boiler when it's not in use but if you don't mind turning valves on and off you can avoid that with some simple plumbing. When I say boiler I'm talking about the heating part of the unit btw, the tank itself is generally separate if you have one at all.
my understanding is that a wood furnace is meant to be used with wood pellets or properly seasoned wood. using random rotting decaying dead wood outside probably wouldn't be a great idea - I'll need to look into it more.
Ok, yes that's true, if you burn wet, green or rotten wood it's going to make a lot of smoke. Wood really begins to rot after the first year if it isn't cut, split and properly dried. If you have deadfall around you that you want to use then you need to process it into firewood as quickly as possible and store it somewhere it won't stay wet.
Not OP, but biofuel combustion is not necessarily better than gas from particulate air pollution or climate metrics.
> Ideally I can build some giant container of sand with some cinderblock, run some copper through the sand, and heat both using the wood being burned. Then, I could pump water through the copper which is being passively heated from the sand into my existing hot water baseboard, but it's unlikely to be hot enough - oh well.
Is that a similar idea to the sand battery in Finland? It was on HN last year.
The author does not mention if their system is air-sourced or ground-sourced (aka geothermal) - ground sourced systems typically use 25-50% less energy and are especially well-suited to places with colder temp extremes where an air-sourced system becomes quite inefficient. Downside is more expensive to install (need to bury a bunch of tubes in your yard)
[1] http://large.stanford.edu/courses/2016/ph240/holmvik1/docs/d...
Just wanted to shout out that this is my state senator, and he does take feedback seriously (and responds to emails quite quickly!). I doubt he will check this thread out but if you email him he will get back to you.
I was wondering what the overall efficiency would be if you still used gas, but had that gas power a combustion engine to drive the heat pump compressor, while also reclaiming the heat from the engine and exhaust? Would that be more efficient than burning gas at a peaker plant to convert to electricity to run the heat pump?
Seems like this exists for non single family home applications. https://www.yanmar.com/global/energy/ghp/vrf/merits.html