An interesting article on swapping away from fossil in home heating

[peakbagger]

John Siegenthaler has an interesting viewpoint on why it is too early to rip out backup heating systems and replace with 100% electric options. https://digitaledition.pmengineer.c...le-heating-design/?oly_enc_id=3970C8130245I4X

My personal experience at home and issues I have heard with much larger recent commercial systems is that the heat pump tech is just not working out as expected in the real world during unusual cold spells. The projects are reporting that the backup systems in place are running more often than design and real world efficiency is lower than actual nameplate.

 

[woodgeek]

Interesting read. As someone who went all electric in a reasonably cold climate (similar to NYC) 12 years ago, I totally get what he is arguing, and made similar decisions myself. That said, I think he has his own biases and its not clear he 'gets' the climate issue.

First, where we agree...

I installed to a low-tech (single speed compressor, no inverter) HP in 2008 as part of installing central AC, but didn't 'trust it'. I had electric backup installed, but disabled calling it from the thermostat (it did get called during defrost cycles by the defrost board in the HP), instead keeping my legacy hydronic oil boiler wired as a second stage on the tstat, for a couple seasons. The oil was cheaper (after oil prices dropped from record highs) than electric strips. Indeed, my HP system started needing backup around 32°F, depending on the weather (dew point, wind). That was about what I had expected looking at detailed tables from the manufacturer AND after doing a very careful load estimate for my house.

I then did a pretty deep energy retrofit DIY, followed by a pro job, that dropped my heating load close to 40%, and meant I only called backup below about 22°F. Since I only spend a few hundred hours below that per season, I ripped out the boiler (this was 2012), and wired the strips in as second stage (but still running the HP at all outdoor temps since its COP >1).

And installed a (early adopter) HPWH, now 10 years old.

At the end of the day, my heating bill was 50% cheaper than previously (bc of the retrofit reducing demand) but my cost per MBTU was about the same (HP+strips versus 84% oil boiler).

But my carbon intensify was reduced about 75% on a seasonal basis, and about 50% on MBTU basis.

As for backup, I was well aware that I could run my boiler on a small genny, but not my HP or strips. So I patched up my old woodstove and verified that it could heat my house in a winter outage. He is absolutely correct that some sort of backup provision is needed. South of Mason-Dixon line HPs already dominate many areas... and surge grid demand during cold snaps. Those grid operators (outside of TX) seem to handle it.

Second, where we disagree....

I have no regrets, and my low-tech device worked as expected. The first compressor got killed by a rare ice storm after 6 years, and replaced with a new one with a much more ice-resistant 'top', which has been purring happily for 8 years. That was a $5k hit. Overall, I think my total operating costs over the last 14 years versus 'do nothing' is a wash... 14 years of oil at 1300 gallons of HHO/year, versus a $10k retrofit, a $17k HP install (including the second compressor), a HPWH, and about 140,000 kWh of electricity. But I saved at least 150 tons of CO2 emissions!

Which was the whole point!

The author you cited works for a hydronic heating company. He is talking about **hydronic** heat pump retrofits. As for hydronic people, they have all drunk the Kool-aid that it is vastly better than forced air. I think it makes sense at a high BTU/h per sq ft corresponding to mid-20th century house design, now its overkill. I switched, and ripped out my baseboards. My house is WAY more comfortable now (bc of the retrofit removing drafts and fixing the balance), and my IAQ is WAY better bc all my air is near HEPA filtered all the time, I have less dust and fewer allergies and I don't have all these ticking and banging baseboards full of dust and spiders lining every room.

I consider the hydronic folks right up there with gas-range evangelists. My induction range will kick their butts in terms of power and control.

You could say...why didn't you do the deep retrofit and keep the oil... ? That would've gotten more comfort and improved IAQ, and come in cheaper than what I did. And still save probably 100 tons of CO2.

Simple: bc I wanted to max my CO2 savings, and not hand wads of cash to evil oil companies, who will shuttle some of it to @ssholes overseas.

So yeah, if you are just about pinching pennies first, and reducing CO2 second, do a deep retrofit and keep the boiler. But I am about saving CO2 first, and this solution cost me nothing compared to doing nothing.

 

[woodgeek]

My personal experience at home and issues I have heard with much larger recent commercial systems is that the heat pump tech is just not working out as expected in the real world during unusual cold spells. The projects are reporting that the backup systems in place are running more often than design and real world efficiency is lower than actual nameplate.

I am personally skeptical of 'cold weather heat pumps' that use the same refrigerant. IMO the BTU output of a (single speed) HP will basically track the vapor pressure of the refrigerant at the outdoor coil temps. Period. Its not due to bad engineering... its physical chemistry. Ofc with inverters, you can make a higher tonnage system and throttle it down at higher outdoor temps to level out the BTU/h. But that is what it is basically, a higher tonnage HP with an inverter motor throttle. Which makes it a bit quieter most of the time, and and gets an eff bump from throttling, but in the end, BTU/h output is still gonna crash at low temps once it switches to going full throttle.

When I did my project, every vendor told me it would never work. They were all wrong. They **unsold** me. I would guess that nowadays there are salesmen trying to SELL these systems. Maybe I'm cynical, but I would expect that some of those guys are gonna gild the lily. Say 'this is a COLD WEATHER heat pump!' so you won't need much backup. Sure. And then when your meter is spinning from the strips during a once in several years cold spell... you feel duped.

Some things never change.

Nameplate efficiency (SCOP) depends on local climate. And historically SCOP has been computed using an Atlanta, GA climate!! Not a reliable indicator IMO.

 

[semipro]

The author you cited works for a hydronic heating company. He is talking about **hydronic** heat pump retrofits. As for hydronic people, they have all drunk the Kool-aid that it is vastly better than forced air. I think it makes sense at a high BTU/h per sq ft corresponding to mid-20th century house design, now its overkill. I switched, and ripped out my baseboards. My house is WAY more comfortable now (bc of the retrofit removing drafts and fixing the balance), and my IAQ is WAY better bc all my air is near HEPA filtered all the time, I have less dust and fewer allergies and I don't have all these ticking and banging baseboards full of dust and spiders lining every room.

I consider the hydronic folks right up there with gas-range evangelists. My induction range will kick their butts in terms of power and control.

I know why I don't like gas ranges and have argued it out with their proponents many times.
What I didn't know until now was why I wouldn't like hydronics. They seem appealing at first but the downsides you mention above are exactly the kinds of issues that leave me regretting a big decision. The creaking and the dust and the spiders -- yikes.
I actually like spiders BTW just not the mess they make.
Also, I've converted just about every device in our house that moves air into a filtration system both for the protection of the device itself (our fridge) and for IAQ enhancement.

 

[peakbagger]

John has some equally convincing arguments for hydronics. He is a PE and consults to several organizations so I would say he is not beholden to hydronics, he is just convinced and makes convincing arguments that it is the best option in the area he is based in.

The problem is its very site specific. Most folks are not familiar with the trend to going with installing a separate indoor air quality ducting with an air to air heat exchanger. The goal is to keep the building internal pressure balanced with the outdoor while supplying a metered amount of fresh air to the living spaces. A HEPA filter is incorporated in the system along with auxiliary heat to make up for the heat loss inherent in the heat exhanger. The flows are much smaller than a hot air system. In the case of Passive house there is no heating system but there is an IAQ system to meet the recommended outdoor air exchanges.

Depending on how well insulated a home is, the heating load is far more than the required air flow for IAQ, The problem with an air based system is the thermal density of hot air is quite a bit lower than water. Its takes a lot of air and space to move the same amount of heat as hot water. Moving large volumes of air is less efficient than the new ECM hydronic pumps so system HP is higher with air. its also easier to zone hot water actively than hot air. The ducts and hydronic pipes need to be in the heated space to reduce thermal losses and duct are going to take a lot more space inside the building envelope.

The big downside with hydronics is that due to the dewpoint issue its best oriented to a heating dominant climate. Air based systems can be used albeit with compromises for heating and cooling.

The other more subjective issue is properly designed low temperature radiant emitters are more comfortable than air systems. I find that when I am heating with a minisplit that I consistently need to run a few degrees higher setpoint than with my admittedly primitive baseboard system. I notice far more stratification.

The debate is probably academic to me as my next house is going to be superinsulated relative to current code so the heating and cooling will be minimal. I will definitely install an IAQ system to get adequate air changes so the debate is what is the best option for a small backup in very cold conditions?

 

[stoveliker]

John has some equally convincing arguments for hydronics. He is a PE and consults to several organizations so I would say he is not beholden to hydronics, he is just convinced and makes convincing arguments that it is the best option in the area he is based in.

The problem is its very site specific. Most folks are not familiar with the trend to going with installing a separate indoor air quality ducting with an air to air heat exchanger. The goal is to keep the building internal pressure balanced with the outdoor while supplying a metered amount of fresh air to the living spaces. A HEPA filter is incorporated in the system along with auxiliary heat to make up for the heat loss inherent in the heat exhanger. The flows are much smaller than a hot air system. In the case of Passive house there is no heating system but there is an IAQ system to meet the recommended outdoor air exchanges.

Depending on how well insulated a home is, the heating load is far more than the required air flow for IAQ, The problem with an air based system is the thermal density of hot air is quite a bit lower than water. Its takes a lot of air and space to move the same amount of heat as hot water. Moving large volumes of air is less efficient than the new ECM hydronic pumps so system HP is higher with air. its also easier to zone hot water actively than hot air. The ducts and hydronic pipes need to be in the heated space to reduce thermal losses and duct are going to take a lot more space inside the building envelope.

The big downside with hydronics is that due to the dewpoint issue its best oriented to a heating dominant climate. Air based systems can be used albeit with compromises for heating and cooling.

The other more subjective issue is properly designed low temperature radiant emitters are more comfortable than air systems. I find that when I am heating with a minisplit that I consistently need to run a few degrees higher setpoint than with my admittedly primitive baseboard system. I notice far more stratification.

The debate is probably academic to me as my next house is going to be superinsulated relative to current code so the heating and cooling will be minimal. I will definitely install an IAQ system to get adequate air changes so the debate is what is the best option for a small backup in very cold conditions?

But one conclusion of "optimal" for a system with that many variables, in general suggests a view that is not complete. There will simply be no single "best" solution as presented for such a large parameter space.

In other words, I do not believe that a system with this many dimensions will have one global optimal solution. Reality just doesn't work that way without neglecting important aspects.

Also, I'm quite surprised about more stratification for a system that actually moves air, creates turbulence, as compared to a system that depends on convection only. Do you have n idea of why you experience this?

 

[sneefy]

Any discussion about mass electrification that doesn't involve a major shift towards nuclear is profoundly unserious.

 

[EatenByLimestone]

I could see it working in a desert. I mean, without trees to fall on powerlines, the system should be much more reliable.

My house was originally built with forced hot air heat. It was converted to baseboard in 81 or 82. I'd love to convert some of it, upstairs, bathroom, and the kitchen, to radiant heat. The other rooms would require tearing out the wood floor and I like it. I really don't want to put it in the floor joists and have gaps from wood shrinkage all over the place.

 

[woodgeek]

I get that hydronic is a very efficient way to move lots of heat, but the higher temp on the radiation leads to lower overall COP, more than negating the gains from lower pumping power. Forced air HPs are still better than hydronic on overall BTU/h.W. The only reason for hydronic HPs is retrofit to hydronic fetishists. And in any climate where you have latent cooling needs, air coils are where its at.

My retrofit airsealing is just at the point where I would need to add an HRV if I kept going. As it is, I run an exhaust blower on a timer during the shoulder seasons (less stack effect). But when there IS a stack effect, I don't mind having excess air filtration for stuff that leaks in.

 

[woodgeek]

Any discussion about mass electrification that doesn't involve a major shift towards nuclear is profoundly unserious.

Depends on the regional climate, honestly.

In a heating dominated climate with poor renewables in the winter (like the US northeast), nuclear can be on the table. Its just a matter of cost vs a variety of other solutions (offshore wind, HVDC lines, H2 or NH3 storage).

In other regions in the lower 48, probably not needed for winter heating.

 

[ABMax24]

It is truly underestimated the amount of energy required to heat homes with electric in extreme cold snaps, Texas found out the hard way. Fossil fuels cope well because the energy can be stored, even with natural gas the pressurized gas in a pipeline is a storage reservoir. Electric just doesn't have this ability, we experience electric supply shortages in the winter during cold snaps, and that's just because we are all using electric to power the fan motor of our forced air natural gas furnaces. We would literally freeze in the dark trying to heat with heat pumps.

Best heating source varies immensely by region, hydronic with storage would be well suited to my climate.

 

[woodgeek]

It is truly underestimated the amount of energy required to heat homes with electric in extreme cold snaps, Texas found out the hard way. Fossil fuels cope well because the energy can be stored, even with natural gas the pressurized gas in a pipeline is a storage reservoir. Electric just doesn't have this ability, we experience electric supply shortages in the winter during cold snaps, and that's just because we are all using electric to power the fan motor of our forced air natural gas furnaces. We would literally freeze in the dark trying to heat with heat pumps.

Best heating source varies immensely by region, hydronic with storage would be well suited to my climate.

Indeed, electricity can't be naturally stored. But specifically re the nuclear issue, solar is stupid cheap, batteries are getting there, and so diurnal storage of large amount of solar energy is feasible and cheaper than nuclear. So day-scale storage of electricity will soon be doable, seasonal storage will likely never be. If your coldest weather is clear and sunny, this works. If your coldest days are overcast (and windless), for weeks at a time, then nuclear (or HVDC lines) look necessary and cheaper than overbuilding storage.

And the TX problem was **ahem** bc the gas pipelines and some of the plants froze bc they hadn't been properly winterized, as a budget move. Other grids throughout the southern US see winter demand surges that they just plan for. Just like the summer AC usage surges. Throughout the southern states ASHPs (and backup strips) are as common as natgat heaters, and they get the occasional cold spell without disaster.

We need to separate bad management from what can be engineered. The TX failure, and the price spikes of electricity and natgas in New England during a polar vortex... are both management failures of electrical and natgas grid operators.

 

[peakbagger]

I could see it working in a desert. I mean, without trees to fall on powerlines, the system should be much more reliable.

My house was originally built with forced hot air heat. It was converted to baseboard in 81 or 82. I'd love to convert some of it, upstairs, bathroom, and the kitchen, to radiant heat. The other rooms would require tearing out the wood floor and I like it. I really don't want to put it in the floor joists and have gaps from wood shrinkage all over the place.

The type of radiant hydronic now used is not your standard slant fin radiator. The new style radiant are either the Euro style panel radiators, in floor radiant which has its limitations and built in wall and ceiling radiant. All three are designed to be operated for longer periods of time at far lower temps. The zone pumps are the new ECM style high efficiency pumps and are variable speed and "smart" with internal logic to control the flow. Outdoor reset is used to control the loop temp. If you look at standard slant fin hooked to an oil of gas furnace, the heat is on/off with thermostat controlling the heat around some requested setpoint. To make a car analogy the desired speed is set on the dashboard and then the engine is turned off and turned on as needed to maintain the desired speed. The aquastat does try to reduce the number of engine/boiler stop starts by using what thermal mass is in the system but most small boilers dont have a lot of mass in them. Add in thermal storage and then the heat source is separated from heating demand. In this case the loop runs near continuously at a lower temp, the thermostat is controlling the room temp by changing the loop temp. Eventually the storage drops down below to a low setpoint and then the heating source runs for longer steady period to bring the storage tank back up to temperature. Once its heating source turns off, it has far lower standby loss than a standard boiler. The storage is lot more efficient if the building can use lower temps. A 500 gallons tank running between 140 and 180 is going to have twice as much heat storage if it can run between 100 and 180.

The big issue with radiant is that This Old House got paid over a series of years to advocate for underfloor and in slab radiant and if properly designed it is definitely an option in new construction but it suffers from the fundamental issue that few people sit directly on the floor. Yes its nice on cold feet if its not too hot but a lot of the floor surface is covered with stuff. The radiant heat flow is line of sight, think of it as the floor being lit up underneath, everything that is not in line of sight of the floor, like your body if its sitting in chair is in a shadow. The radiant heat has to heat the bottom of the chair and then the heat absorbed by the chairs lower surface is then carried by conduction to the top of the chair cushion and then into your body. This works but it means the floor temp needs to be higher. Think of standing outdoors on sunny day in winter, stand in the sun and you feel a lot warmer than standing in the shade. If you are dressed comfortable in the shade you will need to take off some clothes when you step in the sun. Radiant wall panels (also called emitters) tend to be more line of sight, the heat goes in a more direct path to the person. Its still heating up objects in the room and they are giving off heat to the air by convection but the overall loop temperature can be lower. Retrofit radiant panel heaters are a lot less difficult to install assuming the building is relatively tight. If the room is poorly insulated with drafty windows, the amount of heat required will end up requiring the entire wall to be panel rads.

Various experts started looking at what else would work as floor mounted radiant is in the wrong place and panel emitters take up wall space plus they are expensive. What they did was go back to an old method that got a very bad rep and that was integral ceiling or wall radiation. In the old days this was either hot water tubing or electric coils mudded into the ceilings or walls. This was done in homes with minimal insulation and there had to be lot of heat cranking out as a big chunk of it was going outdoors due to minimal insulation. The new thinking (advocated by John Siegenthaler and others) is using materials used in radiant floors in walls and ceilings on well insulated buildings. In this case the interior wall studs are covered with a layer of foil faced iso board and then PEX tubing is attached to it. Sheet rock is then installed directly over the tubing so its in direct contact. It essentially turns the wall into a radiator that is running at a lower temp as there is no sub flooring and flooring to act as insulation. The same approach can work in a ceiling. Yes heat does rise but radiant is line of site and what heat is not absorbed by the people in the room lands on all the surfaces in the room and they convect heat into the room. This approach can be less costly than having the tubing poured in a slab and is far more responsive. Typical radiant floors are left 24/7 at one temp and it can take days to raise the slab temp. Radiant walls and panels are far more responsive, the panel emitters change temps in minutes while the wall or ceiling mounts take up to an hour. This allows temperature setback in non used areas of the home. I know of a few folks who have used this approach in kitchen and baths with the panels in the ceiling and they are very happy with it. The key thing is if the room is full of drafts from poor construction and old drafty windows radiant is not going to work as well as the way to fight drafts is installing lots of convective heat under the sources of drafts to create enough of an upward air flow from the radiator past the window that it redirects the draft coming in from the window.

Once the concept of thermal storage is introduced, standby heat is less critical as the house may be able to go for a day or two off of thermal storage. If electric heat it needed, the utility can easily signal the backup to turn off during peaking events which are normally at worse a few hours. My area is now requiring home sprinklers inn new and retrofit construction and in most cases that requires a big tank of water in the basement for reserve storage for the sprinklers so the next step is use the thermal storage for the sprinkler storage

 

[EatenByLimestone]

Wow, so much information! Its going to take me a bit to pour through all that! Thank you!

 

[woodgeek]

The type of radiant hydronic now used is not your standard slant fin radiator......

Once the concept of thermal storage is introduced, standby heat is less critical as the house may be able to go for a day or two off of thermal storage. If electric heat it needed, the utility can easily signal the backup to turn off during peaking events which are normally at worse a few hours. My area is now requiring home sprinklers inn new and retrofit construction and in most cases that requires a big tank of water in the basement for reserve storage for the sprinklers so the next step is use the thermal storage for the sprinkler storage

I have to agree that thermal storage is a nice feature of a hydronic system in a way that is not feasible with forced air (big box of dusty rocks anyone?).

One could certainly imagine that integrating hydronic storage with a PV powered ASHP running right into the hydronic store would be sensible. The PV and the ASHP would both work during the warmest parts of the day, and no battery (or a minimal one for hour-scale buffering) would be required. In a future world where seasonal electricity load costs are passed to the consumer (so a kWh in New England is more expensive in the winter, and cheap during the summer), which is one in which net metering of rooftop solar is obsolete btw, you could imagine that such a system could be appealing.

Nerd alert: I already think about banking cheap BTUs, bumping my thermostat/ASHP mid-day during warm spring days, and getting the heat back at night when I do a setback. I wish someone could build a smart stat that could do THAT automatically using the weather forecast temps my Ecobee already has on board. A hydronic HP + storage system would be this on steroids, with constant service temp bc you wouldn't be living in your storage.

I'm also down with Euro-style hydronic radiation in a super-insulated house (or multi-unit apt building with a central heat supply). With smart controls you could certainly have a controller that knows both the outside temp (load) and the (perhaps changing) temp of the hydronic fluid (supply) and radiation curve to have a nice steady balance.

I guess I have two feelings about this... From a strictly engineering point of view, there is certainly a lot of cool/eff/comfortable things one CAN do with HP-fed hydronics, that have a place in a future electrified HVAC world. But on the other hand, I think in the long run legacy buildings will get upgraded/replaced with what we would consider super-insulated stock. If the grid operators of the future manage to find a solution for the seasonal storage problem (i.e. HVDC lines) then most homeowners will not want to pay for the complexity of a hydronic system with massive storage, just bc it will eat into their square footage!

Analogy: I think houses are where we were at with cars around 1985. We saw another 20 years of ICE tech improvements, with an impressive improvement in MPG (and peak HP) but at the expense of complexity and cost. And in the end much of it will be replaced with MUCH simpler and cheaper EV drivetrains.

For example, Passive houses were mentioned upthread, with HRVs. IIRC the originators pointed out that HVAC BTUs could be distributed trivially via the same ducting used to deliver fresh air, and that simplification was a goal and a feature early on. Why do I want to have a ton of (even spiffy Euro style) radiation if a 2-3" duct and return to every room keeps me perfectly comfortable? Answer: in climates where that is possible, forced air will reign supreme, in colder climates advanced hydronics will remain.

 

[begreen]

The region makes a big difference. We've been heating with a good 2 stage heat pump system since 2006. The backup heat is resistance coils and our woodstove. We have run on the resistance coils 3 times in the past 16 yrs. and even then it has only been for short runs for a day or two. The woodstove carries most of the load so the system resistance coils only cycle a few times under the worst situation. The heat pump carries the full load when outside temps are 50º or higher.

 

[peakbagger]

I agree entirely that different climate zones will have different solutions. I and John S both are in heating dominated areas so our solutions are going to be different than a cooling dominant area.

Although the physics that water is far more efficient than moving air is not something that can be argued with. The commercial installs I have had a chance to review in Mass are pretty consistent that water is used to move both cooling and heating through the building and then there is local heat pump feeding a variable air volume (VAV) terminal unit to the residences or classrooms. The only air being pumped around the building is the required minimum outdoor air to each terminal unit. This means condensate drains at the VAV but given the price for commercial real estate, big duct systems just do not make sense. Note I also see variable refrigerant flow (VFR) systems that use refrigerant to move the heating and cooling around the building. Most of these publicly funded buildings use geothermal to supply the heating of cooling with some sort of fossil backup. These are also the buildings where they are wondering why they are burning a lot more backup fuel as the geothermal or air source VRF units just are not as efficient as the design expected.