Spacepak Sim-060 Installation Manual
Paskasi Coppola
I don't have the SpacePak but I have what I think is a similar system, a Chiltrix air-to-water heat pump. I heat my house with a combination of radiant coils in the floor and ceiling, and hydronic air handlers. For the radiant coils I have a water set point of 95F and for the air handlers I use 113F.
I only installed the system in April so I don't have a full season of heating yet, when I do I plan to review it for GBA. It also does cooling and we made it through the summer with no issues. The 99% design temperature in Washington is 21F, it was 24 when I left the house this morning and every zone was at its set point with only three of the four zones firing. The real test will be on Saturday, the forecast is for a low of 11F and a high of 20F.
Low temperature hydronic is different. It doesn't feel hot. There are no radiators that are too hot to touch like in an old-school system. The whole house is just at a very pleasant and even temperature.
"comfortable evenly distributed heat" This is definitely the case in older uninsulated homes. Places with rads were comfortable despite the fact that there was zero air sealing and almost no insulation. Places with central air was a combination of a burst of heat and followed by slow freeze between furnace cycles.
Once you fix the air leaks, have decent insulation and use fully modulating equipment, this does not happen. You would be amazed on how even, comfortable and quiet a super insulated house. Since the HVAC will run on low modulation most of the year, there is practically no noise out of the ducts. In most cases you can't even feel the air blowing from the registers unless you put your hand right in front of it.
Most well sealed houses will need an HRV/ERV for fresh air. This means ducting already. Since your envelope is low loss, the airflow required to deliver fresh air is almost the same as you would need to heat, so you are not increasing the noise by using a heat pump.
First place you can cost save is that you will not need a full coverage of warmboard. I would actually run the numbers of your heat loss and output from the emitters. Most places only need about 1/3 to 1/2 of the floor area covered. You would put them only under high traffic areas and by larger windows/doors.
Simplifying your setup, there is no point in heating you domestic hot water with A2W, a standard heat pump water heater is way cheaper only a bit less efficient. If you want more efficient, install drain water heat recovery and you are still less than the cost of indirect+controls+plumbing.
If you want real backup, you are looking at a wood burning stove. If you are only looking at outages of a day or so, a well sealed place will simply coast through. My home looses about 4F in 6hours with the heat off in the winter. If you want heat for longer, upsize the buffer tank, much cheaper than the additional gas burner.
Hydronic cooling is hard and expensive. A slim ducted mini split is about the same cost as your hydronic air handler and more efficient. Here we are back to my initial point, anything that can cool the place can also fully heat it using the same ducts and air handler, so why even mess around with hydronics....
Which gives 90 CFM for a 3-bedroom 2,000 SF house and 157.5 for a 4-bedroom 4,000 SF house, for example. The rule of thumb is 400 CFM per ton for HVAC so that would equate to 2700 to 4700 BTU. You'd have to be super efficient to heat and cool a house of that size just using the ventilation airflow. With an open floor plan, in a tight house, you can get away with one heat emitter per floor, but with a floor that is cut up into bedrooms that doesn't work so well. Where minisplits fall down is bedrooms, they just don't come small enough for the loads seen in bedrooms.
If you want good HVAC distribution you're looking at ductwork. And yeah, the hydronic components are expensive, but right now ductwork is crazy expensive where I am. I just heard from a neighbor how was quoted $70K to replace her oil-fired boilers and radiator with a heat pump and duct work. That's not a typo, $70K. Hydronic installation is work that a person of ordinary abilities (by GBA standards) can do.
Hydronic takes up a lot less space in the house. Most of what I have is 1/2" PEX, which can run anywhere. Houses in my neighborhood are selling for $500 per square foot, if I can save 50 square feet by not needing an air handler room that's $25K.
Main suite ventilation rate is typically 25CFM. Last one I did with a bit above conde min walls and quality double panes needed 34CFM for heat. Not exactly ventilation but close enough that you could use the same duct.
One of problems with hydronics in a PGH is the low flow rates of the fluid. And yes, the floor temperature will only be in the 75f to 78F range. For the lower level slab, PEX around the perimeter should meet the low load.
In terms of cooling a combination of an ERV and dehumidifier should work most of the summer up here in Zone 6A. Too bad residential DOAS are not readily available. A small ducted unit could handle the load. We both agree that you need to design things for low loads.
I have tubing in the floors of the bathrooms, ceilings of other rooms. With my water temperature set at 95F the bathroom floors have a surface temperature of 76F or so, which I think is perfect, it's very comfortable to stand on.
On the second floor I have two bathrooms and three bedrooms, the bathrooms have floor heat and the bedrooms have ceiling heat. I have a two-stage thermostat for the entire story, set so that when the thermostat is set for 70F the floors go on at 70.5 and go off at 71.5, and the ceilings go on at 69.5 and off at 70.5. Most of the time the floors provide all of the heat for the whole floor.
I log run times for each zone. So far for the month of December the floors have been on an average of 15:23 per day and the ceilings have been on an average of just under 25 minutes. So the floors are on most of the time and the ceilings only when it's very cold out. I really like this setup.
So I have a question, how are you running the pumps when the power goes out? Some kind of UPS just for the boiler controls and circulator? A generator? And if a generator which one (because controls often need clean power)?
Cooling is a big gap in Warmboard current offering. It sounds like they are working on a solution. Which is why there is an air handling unit in my PGH design. Love the idea of radiant ceiling panels, but the low cooling load could not justify the dollars, in Zone 6A.
I wouldn't say hydronic cooling is nasty, it's simple: you run cold water through a fan unit. It's very common in commercial space. The real problem is that it offers only slight benefits over a minisplit system in a residential setting, mainly that it's easier to deliver very small amounts of cooling. And you're probably looking at about five times the cost of a minisplit system for the pieces.
I had a look at the Chilltix system - it looks pretty good.
One thing I like about these air to water systems is that it can also produce DHW (which mini-splits can't) and with the Chilltix system it can be run exclusively on solar PV.
DC-Contrarian: Did you add the Chilltrix Psychroligix Dynamic Humidity Control and the V18 Varible Power Backup Heater to your system? What size system did you go with - CX34 or CX50 and which models of air handlers? What did you do for DHW?
I passed on the DHW. I thought it was gimmicky. Basically, when you're in cooling mode it switches to heating mode, heats up the water and then switches back to cooling mode. There's no heat recovery. I have a heat pump water heater, which contributes cooling and dehumidification during cooling season.
I have two of the CS34, the CX50 wasn't available when I designed my system. I don't have the psychrologix. I did go for the V18 but I actually haven't hooked it up yet, I may be sorry tomorrow night.
I have five of the CXI air handlers, three 6,000 btu and two 3,000 btu. One of the things I like is that you can run them on very, very low. You can put the 3,000 btu unit in a bedroom and run the fan on ultra-low and get maybe a couple hundred btu of heating or cooling. That's kind of the knock on mini-split systems.
But the new cold climate SpacePak doesn't NEED expensive radiant floors like WarmBoard or low temp panel rads. Even with 130F output it had decent capacity & efficiency. That is an output temp that can work reasonably with cheap fin-tube baseboard or antique cast iron rads if you have enough of it. See:
With the right controls and a reasonable system design most A2W heat pumps can provide some latent cooling without lots of dripping on plumbing or air handlers, but it can't be left as an afterthought if your average outdoor dew points are north of 60F in summer.
I've been in discussions with a self described "HVAC nerd" in the Boston area who has installed quite a few of the SpacePak Solstice systems and is fully up to the challenge of managing the latent cooling and designing for low temps. His proposed retrofit to my house are still being tweaked, but is a real contender. Another system I'm looking at for my home is the LGs Multi-Vs + Hydro kit, which would take care of the latent loads like any other heat pump. (Samsung has a similar small full- VRF system, but isn't shipping the hydronic modules to the US, so... ) It's a bit harder to find support for LG in my area, whereas SpacePak's factory & company HQ is about an hour's drive from my house, which in this era of supply chain complexity might turn out to matter.
I was looking at the installation manual for the Carrier/Midea dual fuel setups. It seems that all they do is use the Midea thermostat interface module to drive the outdoor unit and remove the TXV from the Carrier indoor unit.
My thinking is that nothing is stopping me from swapping in a liquid to liquid coil for the air handler and using the exact same setup. Based on the outputs, I can get 110F water at rated capacity and a bit less with warmer water.
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