planning for possible future air-to-water heat pump with hydronic baseboards

thomase00

Currently, my home is heated by hydronic baseboards with an oil-fired boiler. I live in the Northeast. I have about 72' of baseboard (plus K84 kickspace hydronic heater) on my 1255 sqft 1st floor, and about 62' of baseboard on my 925 sqft 2nd floor. When I replaced my own boiler 6 years ago, I downloaded my own consumer-oriented Manual-J software and calculated a heat loss somewhere around 45k btu/hr.

I'm planning a major 1st floor renovation that will involve touching most of the baseboard on that floor. Thinking to the future where there will be a push to replace fossil fuel fired HVAC with heat pumps, what should I do to prepare for that possibility when replacing baseboards on the 1st floor? Are there specific baseboards that we should use that operate better at lower temperatures (i.e. 120F)? If we replace with baseboards optimized for lower temps, does that preclude running them at higher temps for the time being?

I already inquired about radiant floor heat and that might be too expensive for the scope of this project.

I replaced central AC about 4 years ago, but the AC system is a retrofit added after the house was built and doesn't hit every room in the house, so swapping to central heat pump is not necessarily a viable solution for whole house heating in the dead of winter.

Jamie Hall

I would at least consider using high output baseboards. They are usually an option. Now whether you will be able to fit enough lineal feet of them into your floor plan I couldn't say -- but you can figure out where to put them and add them up.

The relationship between heat output from a baseboard or a radiator isn't quite exactly linear, but for all practical purposes using a linear relationship is probably close enough, in which case you can use the relationship actual BTUh output is equal to 240 times EDR times (average water temperature minus space temperature) divided by 150,

Dave H_2

Yes, design for as low temp as you can. Target a high temp of 125F. search for hi-output baseboard. There are many of them out there and many ways to install here are two that I have designed around Runtal and Heating Edge 2

hot_rod

Some ideas here.

https://www.caleffi.com/sites/default/files/media/file/idronics_25_na.pdf

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water heat pump systems.pdf

ElliotFirestone

I threw together a simple EDR calculator you can use (make a copy) with a room by room load calc.

Here's a Siegenthaler video on this topic.

You might consider Hydronic Alternatives baseboard product combined with panel radiators. Heating Edge looks nice as well. Both are included in the EDR calculation spreadsheet, along with type 22 and 33 panel radiators.

For ODU, I'd consider the Enertech Advantage, which you can use in a heating only application without using glycol or buffer tanks, which can reduce operating efficiency. RenewaBoiler is also worth considering, particularly if you live in a cold climate.

I like the design philosophy of HeatGeek from the UK, who offers training and has installed SCOPs exceeding 4.4 for heating only applications including domestic hot water.

Energy Star for "Heat Pump Boilers" should be available later this year, which would make an A2W system eligible for $8k of federal HEAR incentives capped at 150% AMI. If you make more than that, you can still get $4k from the HOMES program.

If you live in NY or MA, you can get $10k of incentives now for full electrification, and slightly less in Vermont, and other states will offer incentives once the Energy Star certification is in place.

WMno57

ElliotFirestone said:

For ODU, I'd consider the Enertech Advantage, which you can use in a heating only application without using glycol

Is that a monobloc design? In the event of a power outage or component failure, how long before one would have an expensive Heat PumpSicle on the side of their house?

ElliotFirestone

Yes, it's a monobloc. Antifreeze valves are available, and the existing designs are pretty simple.

I'd like to see a antifreeze system that doesn't dump water outside in the event of a power failure. What do you think the best design would look like?

WMno57

For a home with an Air-to-Water HP, I think the only prudent designs are either a split system, or monobloc with glycol. With a monobloc, one could have a heat exchanger inside the home to avoid pumping glycol throughout the home.
For a large institution with backup power and 24x7 on-site building operations staff, then straight water and dump valves might be OK. Of course as soon as you design a system and operations plan that is idiot proof, someone becomes a better idiot . Like the guy I worked with that saved a few nickles on heating the enclosed loading dock, but spent $$,$$$ when the fire protection system froze.
No way I would rely on those valves to work on my home while I was away in the winter. My opinion, they are gimmicky.
Is running a monobloc on straight water something that is seriously suggested by climate activists?

Hot_water_fan

Is running a monobloc on straight water something that is seriously suggested by climate activists?

Please don’t make this about politics. We can agree that a mono block doesn’t make sense with glycol in freeze prone places without torching another thread. 

Nick_Castrads

@thomase00 I'm currently designing an air-to-water heat pump system for my own home. I'll be using a mix of new and reclaimed cast iron radiators.

There is a really terrific channel on YouTube (a Brit like me, I'm afraid) called Heat Geek. I'd also check out videos by a superb plumber called Szymon Urbanek - his channel is called Urban Plumbers. I've learned a lot from them.

In my home (an 1895 townhouse in Manchester, England), we're first of all insulating everywhere we can, installing triple glazing (the windows need replacing anyway), and fitting Mechnical Ventillationn & Heat Recovery throughout as part of a major reno.

This reduces peak heat load from approx 6000 BTUs/ sq ft to 2000 BTUs / sq ft.

The radiator output at MWT125ºF is about 40% of what it would be at MWT 170ºF, but with the reduced heat load we should bring down the requirement sufficiently that the radiator sizes are still quite a lot smaller than they would be in a regular 170ºF MWT installation.

Would love to hear how you get on as you progress with your designs.

PeteA

Is the air to water heat pumps main purpose to get the water temp most of the way close to the systems design temp and then the boiler or other heating system takes over from there? So basically the air to water is used to head a volume of standby storage tank water up to its max output and then the main heat system takes it the rest of the way? This is a pretty interesting idea if the waste energy from the air water heat pumps fan can be used for a secondary purpose it seems like this would be a win win. Like putting the air to heat pump physically in a garage or other unconditioned space in the house would that by product also "warm" that space a little?

WMno57

PeteA
Air to Water HPs can heat a space all by themselves. No boiler needed. Most AtWHP available now in the USA output water at a temperature cooler than traditional boilers. So everything else being equal, you need bigger emitters. Radiant floors need a lower temperature (to keep from baking your feet) so AtWHPs are a good fit for this.
Locating a heat pump inside conditioned space cools the space. Just like a fridge. All it does is move heat from one space to another. Heat pumps don't make heat, they move heat. A fridge is a heat pump. It doesn't make cold, it removes heat from inside the fridge and sends it into the kitchen.
Not much waste energy to capture from the fan. I suppose if you wanted space cooling, the heat pump could contribute to that. An example would be a heat pump water heater for domestic water in a basement. It would both heat domestic water and cool space.

PeteA

Thanks @WMno57 appreciate the info
This is a really interesting new tech and the low electric usage seems like a good benefit to shave off the expense of other heating and cooling systems by combining these systems.

exqheat

Remember design temperature is for a 15 degree day. How often does that happen any more. You can heat with lower temps during moderate periods. Keep the fossil back up for power failure and extreme cold.

Jamie Hall

To go back to the actual original question that @thomase00 had -- what should be done to prepare for eventually fitting a heat pump -- we go back to the various answers which got somewhat buried: figure out how many lineal feet of high output baseboard he needs to meet the heating requirement of the structure using 120 F water and install them and, if necessary, add enough panel radiators at the same temperature to make up the needed difference.

Then, when and if he decides to, he can switch to a heat pump.

hot_rod

The time to switch over to another fuel can be automated also. That function in built into some of the HP controls. No need to guess when the time is right.

Data like this for Boston, helps make good choices.

Hot_water_fan

 If we replace with baseboards optimized for lower temps, does that preclude running them at higher temps for the time being?

Nope, you’ll just have a more responsive system! 

hot_rod

My goal would be cover a design load with SWT at 120f. So #1 you need to know room by room load. #2 chose the heat emitter that can accomplish this.

Usually radiant floors, walls, or ceilings are the lowest requirements. Panel rads or high output baseboard also. Fan coils can be sized down to 120F. Most kickspace heaters come with a 110 and 120° snap start to stat the fan. So 120 SWT would work with some wall or kickspace heaters.
Jaga makes a blower assembly that adapts to many of their radiators, working down to 90F. Runtal also has a fan assisted for low temperature applications

Myson used to build a fan coil that tired directly to solar thermal arrays. SolarVector maybe?
Once the fluid hit 110 or so they would start the fan. I would guess a 5° or more differential, so fan running as low as 105 coil temperature.

Radiant walls and ceilings are great heat emitters, no furniture or coverings to reduce output, just the r-value if the 1/2' sheet rock. And plenty of walls in a home to turn into radiators.

https://www.pmengineer.com/articles/91631-a-sampling-of-low-temperature-heat-emitters