Water-cooled fan coils or water-cooled air handler
We have a 1500 sq ft (evenly divided bw 1st and 2nd floors) brick century home in Cleveland OH. We are well on our way to getting the house to Pretty Good House standards. We have an efficient hydronic heating system with homerun, low temp wall rads.
We would eventually like to lose the natural gas, but cannot afford to at the moment. We’re currently undergoing a modest renovation, and I’m roughing in HVAC for future upgrades including ducting for an ERV.
I was wondering if the GBA had recommendations on whether to (eventually) cool with either individual water-cooled fan coils or a water-cooled air handler, as this will dictate running condensate/pex or ductwork. My future dream system is based on this article:
Thanks!
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I like the 1 air handler per floor approach. Air handlers do better with filtration and usually dehumidification. They’re also quieter vs. multiple ductless fan coils and I think ductwork is generally easier to look at. Also easier to swap over to an air to air Heat pump in the future if needed
Makes sense to me, thanks!
On the cooling side, there’s not really an advantage to using water besides potentially some savings on DHW if using a desuperheater or similar, so splitting that up might make sense for you. You’ll always have an efficiency hit with air to water vs air to air.
I’ve had that thought, too, and may go that route. I just like the idea of one heat pump to rule them all. As our house is already plumbed for hydronics, I was thinking hydronic cooling would be nice. I’ve also thought about just roughing in for ductless mini splits and making it easy for a sooner upgrade. The redundancy of heating was putting me off, only because it seems wasteful. Having a ductless mini split for cooling may be the most cost effective option, even if we have a great hydronic heating system.
If I had done things differently, and had realized how much we were going to have to tear our house apart for structural repairs, I probably would have done a ducted heat pump for heating/cooling needs. At the time, putting in a hydronic system was infinitely simpler without having to tear everything apart.
Air-to-water heat pumps have come a long way but are still pretty experimental. You won’t have good luck finding service/repair people to work on them but if you’re willing to be a guinea pig they can be pretty efficient. About the same COP as a modern air to air heat pump but there are some with more clever controls like the Chiltrix where it will purposely produce warmer water for cooling if it knows it does not need the dehumidification and that will boost its COP. If you need dehumidification you will need fan coil units and/or a dedicated dehumidifier which requires some ductwork. Might also need ductwork for ERV.
We’re probably at least five years out from being ready for a heat pump—our house has required a lot of capital, and in the interim heating with our boiler and using a couple window a/cs is fine. I’m just trying to plan for ahead while the house is ripped apart. Hopefully by the time we’re ready there will be more options. I’ll probably run lines to the upstairs just in case. Thanks for the input!
Do you currently have cooling?
Looking at the climate stats (https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf ) it seems that in Cuyahoga County you're pretty strongly heating dominant, twice as much heating as cooling. I bet you also have a lot of humidity in the summer. If you need to remove humidity you have to pass air through an air handler with a condensate drain, there's just no two ways about it.
As a broad design goal, you want to size the air handlers for the cooling need in summer, and then supplement with some other form of heat in the winter. What that other form is depends on your situation. Also, you need to think about ventilation in a tight house, and your ventilation strategy is part of your combined strategy.
In terms of cooling, the mainstream choices are ducted vs. ductless. The advantage of ductless is it tends to be cheaper and simpler. The downside is that they work best in big open rooms, in small rooms it can be hard to get them to turn down enough. They work best when you have one compressor per head; if you have a lot of zones you end up with a lot of compressors or you have to put multiple heads on each compressor, which makes the turn-down problem even worse. The downside of a ducted system is the ducts, which take up space inside the house and are expensive, I'm hearing about quotes of multiple tens of thousands of dollars for full-house ductwork.
Air to water is an out-of-the-mainstream choice. I have a Chiltrix system in my house. It uses AHU's that are similar to minisplit heads, but since it's water you can also use it with radiators and radiant heat. It doesn't suffer from the sizing issue of minisplits, you can have one compressor and as many heads as you want, heads come as small as 3000 BTU/hr and there's no penalty for oversizing. A single room with a single head works really well. The big downside is the price, everything is really expensive. The heads are also somewhat larger than equivalent minisplit heads, and they're not the best looking to my eye.
DC, how well do you air handlers work at dehumidification in your climate? I'm very familiar with the area down there, since I've spent a lot of time going between Baltimore and DC with contract projects. Lots and lots of humidity. A regular A/C unit will generally run the coils at a lower average temperature than an AHU supplied with chilled water will, so I'm curious how well your system does at bulling down indoor humidity levels.
My experience with cooling in that region is mostly with datacenter systems, and those run cooling so much just to remove the heat from the facility (which can be in the multi-megawatt range), even a small amount of dehumidification is effective since the system is running continuously, 24x7. A typical residential system will cycle and have much shorter run cycles (datacenters don't really have "cycles" with the cooling system), so it probably runs differently from what I've seen.
Bill
I have struggled with dehumidification. I turned the water down as cold as it would go, until the chiller shut down because it was hitting 32F and freeze protection kicked in. Since I have propylene glycol in my fluid I got the secret configuration from Chiltrix to bypass the freeze protection and turned it down another couple of degrees.
Even so it struggles, with humidity in the high 50's downstairs and low 60's upstairs, which is higher than I would like. I'm trying to figure out if it's the AHU design or something in my configuration.
You might try lowering the airflow over the coils for better dehumidification. You have to be careful the coils don't freeze up if you do that, which isn't normally a problem with an AHU, but might be if you're running an extra-cold loop.
In datacenters, we usually optimize the overall system operation, and that's easier to do since our facilities tend to operate in a near steady state most of the time. We like ~70*F or so air in the datarooms, usually around 40% RH or so, and the chilled water supply is normally in the low 40*F range. The AHUs modulate the flow of chilled water through the coil with valve, which does most of the temperature control work, but we also have some adjustment range for airflow with the newer equipment. It's possible to find a balance where you keep everything around the optimal operating range (which is our goal at work, since it's the most efficient way to run things), but it's difficult to do that in a typical residential system that will cycle a few times and hour or so.
Bill
Thanks for the input. We’re currently getting by with two window ac’s. One 14k downstairs and one 14k upstairs are sufficing for now until we can afford to go all electric. I just want to get things in place for the future while the house is ripped apart.
Mainly I want to know if I should be running a bunch of water lines or plan on ductwork down the road (we’d do one air handler on each floor as suggested above for simplicity of ductwork…ductwork can be added later as both 1st and 2nd floors can be easily ducted).
Pardon my ignorance, but are the Chiltrix heads serviced by (insulated) 1/2” water lines? I have come across their products and am intrigued. I hope by the time we’re able to swing an upgrade there will be even more options.
The Chiltrix heads are fed by 1/2" water lines, I use PEX.
I wouldn't run them now, if ducts can be added PEX can be added, it can be fished through walls. The problem with future-proofing is nothing is harder to predict than the future.
I love John Siegenthaler, but I think he's behind the times here. I have a Chiltrix air-to-water heat pump, and I've found the controls that it comes with are really quite sophisticated and impressive. It has a modulating compressor, and what it tries to do is modulate the compressor speed and the water circulator speed so that it runs continuously at constant output, which is the most efficient way. You configure it with the water temperature you want, it modulates the circulator pump so that with that water temperature the return flow has a 10F delta. It then modulates the compressor to match the heat flow to the water flow.
It does have a minimum modulation of the compressor. If the demand for heating or cooling is lower than the minimum modulation it will cycle on and off. It has a buffer tank so when it cycles on it will fill the buffer tank with heated or cooled water, and then when it cycles off the system will continue to draw from the buffer tank until the temperature drops to the point where it cycles back on again.
I used it with a 3-pipe buffer tank. With heat pumps, efficiency is all about delta temperatures. The water coming off the compressor in heating mode will always be hotter than the buffer tank, you don't want to lose that hotness by mixing it with the buffered water. If you don't need buffering you want to cut the buffer tank out. In a 3-pipe system the water from the heat pump goes to a tee, with one side going to the radiators and one side going to the buffer tank. If the heat pump is modulating, the radiators are pulling from the output and no heat goes into the tank. The return from the radiators goes into the buffer tank, and the return to the heat pump pulls out of the bottom of the tank. So if the radiators aren't dissipating enough the buffer tank will warm up, eventually the heat pump will shut off. The radiators will continue to pull from the tank.
In heating mode it has built-in automatic outdoor reset, where the warmer it is outside the cooler the water it produces. This makes it more efficient, with a smaller temperature delta, and allows it to modulate lower.
In cooling mode it has an option to sense indoor humidity and produce water that is only as cold as needed to dehumidify. This is similar to outdoor reset conceptually. This is an extra-cost option and I decided not to install it; in my humid climate I run the water at the coldest setting all summer long and just barely get enough dehumidification, I typically see humidity in the 57%-61% range.
DC, I'm close to where you reside (No. VA) and have been intrigued by the Chiltrix sytems myself. A few questions if you don't mind. Is there an installer you would recommend for the area? Would you say that one would need a very well insulated house that allows lower heating water temps for these systems to work as well as advertised? You said the AHUs (which I assume operate somewhat like fan coil units) are ugly. Which products did you go with? My understanding is that the Chiltrix units are compatible with other fan coil units. Is that correct? Finally, have you found them to be as efficient as advertised? And would you install them if you were doing it all over again?
Hi Antonio.
I installed my system myself, I don't know anyone who installs them. In DC all HVAC work has to be done by a licensed professional -- or under his supervision. I'm not licensed, but I got someone I know to pull the permit and "supervise" my work.
It definitely makes more sense on a better insulted house. With heat pumps, the costs go up pretty linearly with capacity, unlike fossil fuel burners where often the only difference between different capacity burners is a different jet. My house has a design heating load of 28K BTU/hr at 21F and I have two of the Chiltrix CX34's. You may remember last year right before Christmas it got down into the single digits, my two units were putting out a combined 34K BTU/hr which is right around their rated capacity at that temperature and just barely maintained temperature. (Specs are at https://www.chiltrix.com/CX34-air-to-water-heat-pump/ ). I have a pretty efficient house, a lossier house might need more units, and they're about $4900 each so it pretty quickly becomes ridiculous.
For the AHU's I'm using Chiltrix CXI series fan coils ( https://www.chiltrix.com/chiller-fan-coil.html ) . I don't know what the distinction is between an AHU and fan coil. I have the 3K and 6K BTU units. All are ceiling mounted. The 3K is actually really sweet in a small room, it's whisper quiet and holds the temperature steady. The units that Chiltrix sells are rebranded, a lot of people sell them, I think they're manufactured by PHNIX.
One of the beauties of hydronics is that you can mix and match pretty easily, hot water is hot water and cold water is cold water. Unfortunately there doesn't seem to be much of a market for fan units in this country. Hydronic cooling is standard in commercial construction, but most of those units are way too big for residential. On Ali Baba there are literally thousands of fan units for sale but I'm a little hesitant to buy a pig in a poke.
Thanks for the input, everyone. For what it is worth, I emailed John Siegenthaler.
He recommended a single air handler for minimizing cost and maintenance. Balancing or zone dampers could be used to split air flow between floors. He recommended Enertech or B&D air handlers.
That seems like an odd recommendation. To me the big advantage of hydronics is the ability to deliver small amounts of heating and cooling exactly where you want it. If you're just going to go with one big air handler per floor why not just have a conventional heat pump? It's a lot cheaper.
I see what you’re saying, and the ability to dial
in the cooling is a boon.
I think he as emphasizing the most cost effective and simple solution for specifically what I was proposing: an eventual air-to-water heat pump for DHW, to heat water for our panel rads, AND cooling. The air handler we’d need for our house would be around $2k +/- (not including duct work). That doesn’t add much to the cost, and will provide better mixing in the summer and help to further dehumidify the house.