VRF system with pool heat zone?

DIYorBust

I'm contemplating replacing my AC with with a heat pump system, I'm anticipating a heating load of 100-150kbtu at design temp, which I would like to achieve. Now if I do this, I may get about 7k(hope this is not a violation, it's not really a pricing number) in incentives. But, I also have a pool that I would like to heat, and a good pool heat pump is expensive to buy and install, plus needs it's own electrical. So what I want to do is design a VRF/VRV system with a pool heat zone. In the heating season, the pool is closed, in the A/C season the pool can be heated with A/C waste heat, and in the shoulder season the system can use the extra capacity from sizing to the space heating load to heat the pool. It seems like it should be possible to use an appropriate heat exchanger for this purpose, but would manufacturers allow this? Some device would need to call for heat to the exchanger. Mitsubishi does have an air to water heat exchanger for City Multi for instance, but that would have to then go through another heat exchanger that was rated for pool water. This system would potentially reduce pool heating costs, installation costs, and improve both pool heating and space cooling efficiency, and possibly reduce wear and tear on the outdoor unit. Is it possible?

Thanks!

pecmsg

150K BTU/h heat pump is HUGE!

Kaos

150kBTU heat load with recent code min construction in colder climate puts the house at around 10000sqft. If your place is not that big, you might want to tighten that number a bit.

What you are looking for is heat recovery units. These are common in commercial space but pretty rare in residential.

The one I know about is the 5 ton unit here:

https://www.lgvrf.ca/en/products/air-source-units/multi-v-s

This comes with a hydro kit that can do water heating from recovered cooling heat. Not sure if you will find an installer though as it is semi commercial.

A regular heat pump won't work for what you want.

hot_rod

even if it is 150k , that is not much capacity for pool heating. More like a hot tub heat load.

DIYorBust

Thanks, for the responses! Yes 150kbtu is large, the house was built around 1920, with updates most likely in the 1980s. I will have Manual J done, but doing it for an attached rowhouse of about 3200 sq feet came out around 80kBTU, so I have to guess this freestanding home, probably around 3000 sq ft, more if you ask a real estate agent, will be at least 100kBTU. Could be wrong but I'm thinking a 10 ton system could do the job. Maybe a 5 ton could, but I think I'd be light, open to input though. I currently have a 250kbtu steam boiler and cast iron radiators. It obviously doesn't run continuously. I want to get a sense of whether the project is feasible before I hire someone to formally do the manual J, since many of the HVAC installers can arrange this.

DIYorBust

Thanks, I was not aware of the LG Multi Vs. But I suspect that most hot water application is not intended to process chlorinated pool water, so an additional heat exchanger may be required. Do you think this might be an appropriate solution?

DIYorBust

https://forum.heatinghelp.com/discussion/comment/1855524#Comment_1855524

Fair enough. The largest electric pool heater heat pumps I would say are normally available for consumer use are about 150kbtu, comparable to this size. I already own a 115k pool heat pump, and in the shoulder season it can take 48 hours to bring the pool up to temp(but it does the job). I have to figure standby losses are significant during the warmup. I think with the 150K system in parallel, I could get pretty good performance out of it. A propane heater might be around 350-400KBTU. Keep in mind I'm only heating the pool when the lows are at least around 50-55 at night and the water is usually over 63 degrees. Save for some odd weather patterns, it's usually too cold outside for us to want to use the outdoor pool below that, and I wouldn't bother heating it.

tim smith

Any month now Daikin is to release the new Altherma 3 Or ?4 , not sure what # the model is yet for USA. It will be air to water heat pump like the original altherma. Have higher temp capacity. That might suit your needs. Maybe do a water to water heat x in cupronickel for the pool. Even if you don't hit ideal heat up times would still work for you. I have been waiting for the Daikin to show up for my place.

DIYorBust

https://forum.heatinghelp.com/discussion/comment/1855598#Comment_1855598

Thanks Tim, so I'd be using a glycol mix for the interior space heating/cooling zones? Look interesting, but the literature for the current model shows only little babies that can do around 7.8kw, or 26kbtu.

Kaos

A regular air to water won't get you heat recovery. For that you need either a real heat recovery system (these usually have 3 pipes so any indoor unit can either cool or heat at the same time) or you need a water to water unit where you are dumping house heat into the pool directly.

People tend to way overestimate heating and cooling loads. I have pretty hot muggy summers, around 3000sqft with reasonably sized newer windows would have a cooling load around 2.5 tons and that is on the hottest day, rest of the time is well bellow that. Free heat if you can get it into the pool for cheap but also won't do all that much.

DIYorBust

https://forum.heatinghelp.com/discussion/comment/1855609#Comment_1855609

That's correct, but the point is also to use the system to actually generate heat for the pool even when the AC isn't running. 5 tons is 60kbtu, I can't see that being enough to heat the house on an 11 degree day which is usually the design spec here, even if it's a cold climate heat pump. A pool heat pump should cost about the same as adding 5 tons to the house heat pump, why pay twice, and I'd get more tax credits and incentives that way, and can probably afford to get a good a good shop to do it.

Alternatively I can buy a 4 ton midea mini split or two and get 8 tons for rock bottom cost, and install it DIY in a weekend. Come on folks, why are we going to give this business to China?

Kaos

11 degree is not that cold and not a lot of regular houses have an above 60k btu heat load.

Roughly how much fuel did you use over last winter? Rough heat load is fuel used in Therms multiply by 42.

So you used about 1420therms, then you heat load is 60k. For more exact number run the math here:

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Air to water for space heat only makes sense if you have existing low temp emitters like panel rads or floor heat. If that is your case, you can definitely re-purpose the a cold climate air to water unit with an extra heat exchanger to heat your pool in the summer. It won't be taking house heat to do so though.

DIYorBust

I use oil, and I'd have to check, I'm pretty sure I used more than 1420 therms, we have oil, but I think your, but I don't think it's wise for me to calculate the heat load this way. Because if I switch from a 250kbtu steam boiler to a heat pump, the steam boiler will have no problem maintain 72 on an 11 degree day, or even a 5 degree day. With a strict design temp of 11, that's allowing for some days where it will just be colder than 72, and we'll have to bundle up, or cook all day, or make a fire. It's very windy where we are, on a tall hill near the water. Even if 60k is the average used in winter, I think that system will struggle to keep up in january and february, but that's for the manual-j to tell us. If it's 60k, then fine. Another consideration is thermostat setbacks. If the recovery time is 24 hours, that's not very practical. We do not spend full time at this location, I normally keep it at 55 when I'm not there, I frequently bring it up to temp in the winter, and that currently takes about 3-4 hours, but it would not be very efficient if it took say 48 hours.

So I was hoping to do a professional solution using a VRF system, which might even be able to do other things like make DHW, or dehumidify. But if it's a bridge too far, I wonder if I could use a titanium refrigerant to pool water heat exchanger with the midea system. Hotspot energy makes one, there are others on the market. But it would take some "engineering" to figure out how to control it, so that the pool could call the system for heat, and the system would never run cold refrigerant through the heat exchanger. Perhaps an air handler with a disabled fan could do the heat call. The hotspot controller can bypass the exchanger for temp met or no flow, but would have to find a way to get it to recognize the loop is in cooling mode. Probably could do it with automation tools available, not a great system at all compared to say a Daikin VRV or City Multi that is designed to do it, but seems hard to find a pro who wants to build a VRF system on a this scale.

TAG

I think you will find that the cost to do what you want is more than the payback … what kind of a heat pump pool heater do you currently have that can put out 115k BtTu's ?

Nothing is going to give you the same comfort in an old house like the current steam system — even converting it to hot water (if even economically possible) is still going to need very hot water in most cases due to the radiator sizing on the coldest days.

This becomes an even greater issue when you want rapid recovery .. heat pumps are not sized that way.

I'm assuming you plan on having a variety of mini-split type heads products throughout the home?

FYI — 7k worth of incentives will be a rounding error with some of the systems. I love mini-splits — singles. They are great problem solvers .. I don't love multi head system for a couple of reasons. First — they must be installed by a company willing to do the proper calculations and one who really understands them. Second — they are a nightmare when something goes wrong …. like a leak.

I have a 20x40 pool at my place in NJ and it need 400k — thankfully we have natural gas at that house,

I have had second homes/ vacation homes for most of my life … I get the issues and problems of heating a home that's empty most of the time. Your problem is you still want it to be comfortable when you are there. My guess is when you really crunch the numbers the BTU's from any heat pump system is not going to be there in any meaningful way.

I had looked into it in NJ years ago. When do you need heat to the pool … when it's colder? That is the same time the house needs the heat (we open early and keep open late). In the summer when the AC system would be throwing off the most waste heat — the pool does not need it.

Now —making a zone for the heat pump. To take all the heat from the system .. no system I saw was able to do that and no one made a refrigerant to water exchanger suitable for a pool.

DIYorBust

Thanks Tag,

Just to clear up, you can heat a pool with a heatpump and it has some very nice advantages. he aqual SQ200R can produce 138kbtu at 80 degrees ambient, or about 88kbtu at 50 degrees. They also make a 500kbu version for commercial applications, but it requires a 150 amp circuit, and has a much higher cost that makes it not really suitable for home use. Of course that is impacted by the outdoor temp. I have an aquacal SQ125VS variable speed heatpump that can produce 115kbtu of air to water heating, they make versions that can do up to 140kbtu. If temps are above 55 degrees, I can raise the pool water temp by about half a degree per hour, faster if I put the solar cover on.

We don't have natural gas, we can use propane or oil in my area. Nobody uses oil for pool heat, most use propane, but it's expensive. The heat pump is much cheaper to operate. I'd guess it can maintain pool temp for about 1/3rd what a propane heater can, maybe less depending on outdoor temp. It never runs out of fuel, and doesn't require installation of a huge fuel tank, and it produces no exhaust. If we had natural gas that would be an option to evaluate, but we don't.

We don't really heat the pool during the heating season. During the should season, when temps might be in the 60s during the day, but drop to around 50 at night would be about the limit. We really don't need to run the space heat in this scenario, and I could use the heating capacity in the pool.

Now also it should be mentioned that a VRF system like mitsubishi city multi or daikin vrv can do this heat and cool simultaneously different zones and are designed for this purpose. Mitsubishi does make a heat exchanger for the city multi, not sure about daikin. But the water would have to go through a second titanium heat exchanger, which doesn't sounds very efficient.

winnie

https://forum.heatinghelp.com/discussion/comment/1855527#Comment_1855527

What is your existing heating system.

My house has an oil steam system. 144 kbtu, probably set by matching radiator sizes and an installer who just said 'bigger is better…'.

I put an hour meter on the system, and figured that on the coldest days (we had a cold snap that came out colder than the expected design days) the boiler was going less than 1/4 of the time.

If you monitor your existing heating system you can get a much better evaluation of the actual heat load than any calculation can provide.

winnie

Sorry, I see you already answered about your heating system and winter average fuel consumption.

I absolutely agree, you can't determine your peak heating demand from your total fuel consumption. It is like trying to figure out your peak electricity demand from your monthly electricity bill.

What is useful is to put some sort of monitor on your heating system so can calculate boiler burn time on a daily or more frequent basis. I just use a cheap 'hours' meter in parallel with the burner blower; on the coldest days I checked how many hours the boiler ran each day. A 'home energy monitor' with a CT on the circuit feeding the boiler would also give you this information. Lots of ways to skin that cat.

If you know the number of hours that your 250 kbtu/hr boiler fires on the coldest day (or the design day, or on a cold but windy day), you pretty much know how many btu it takes to keep your house warm.

DIYorBust

Interesting, does anyone have a recommendation for an engineer or service that can do a manual j from plans? Not sure how reliable that would be, but might give me some sense of where it shakes out.

I can pull the data from the ecobee, but one issue is that I keep the house at 55 much of the time, so may be a little tricky to establish what the actual usage might be on the coldest days.

I think it is not a terrible guess that it will come out around 100kbtu, and it wouldn't kill us to go a little bigger given that it will likely be a modulating system and the heat pump specifications are probably a little aggressive on what they can produce, particularly on very cold days.

DIYorBust

I believe I've made some progress here. I'm now contemplating using an air to water heat pump such as the Apollo 6 ton air to water heat pump, and using hydronic interior air handlers instead of evaporator coils. The hydronic system seems easier to manage in many ways, pex could be used, new devices can be replaced or added by a plumber without the need to vacuum down the system or deal with brazing and refrigerant. It's also possible to use fan coils and heat exchangers, or maybe even radiators, without being limited to the units produced by the outdoor unit manufacturer.

The unit can then use a hydronic heat exchanger to heat pool water, and indeed apollo makes such a unit recommended for this exact use. So the unit can easily use titanium heat exchanger to heat the pool water, without needing to daisy chain two heat exchangers. So that could give me an extra 6 tons of pool heating capability.

But can I accomplish the goal of heat recovery? Maybe. The unit is not designed for heat recovery, but I'm wondering if I could install a refrigerant to water heat exchanger on the existing pool heat pump to make chilled water for the hydronic loops. That way if the pool is heating, the house heat pump will not need chill water. I'm uncertain if I could also get the house heat pump to heat the pool while the house is being chilled, because I would need a control system that could isolate the chilled water loop from the pool heating loop. Another drawback is that heat recovery would be available only when the pool is being deliberately heated, whereas ideally whenever air conditioning is used it would just deposit waste heat into the pool providing a benefit of extra pool heating even when we might not have otherwise wanted to call for pool heating.