DIY radiant heating/cooling +DHW system. Will it work?

Jimmie

I am a homeowner with no plumbing training and I'm completely overhauling my house. I have designed a system for radiant heating/cooling and DHW.

Details: 1,300 sq ft house in Bozeman, MT where we get -30F temps in winter. I attempted a Manual J and get results between 40k-60k of heat loss at -12F. I already have the radiant loops installed with Warmboard panels on the ceilings. I prefer not to use Warmboard Comfort System or any other combi boiler because a combi would be oversized for my space heating yet at the same time inadequate for filling a bathtub in winter (groundwater temp is 36F).

Questions:

1. Does my pipe sizing look good? I am wondering if a 1" hydraulic separator and 1" headers would be sufficient, rather than 1-1/4". If the boiler has 1" piping but I'm also running the DHW loop into it, do I need to upgrade boiler pipe to 1-1/4?
2. What pump should I use for my radiant loops with just one zone?
3. What pump should I use to circulate the indirect DHW loop?
4. Is it feasible to run my entire house as one zone and then fine tune the temps in bedrooms and sunroom with Caleffi Quicksetter balancing valves?
5. Any ideas how to prioritize the heat pump in milder weather and automatically switch to boiler when it gets too cold for the heat pump?
6. It seems to me that in summer the whole system could run cold water for cooling and not affect the boiler-DHW loop which is hydraulically isolated, and not have to use any fancy switches or diverters, correct?

Thank you.

Hot_water_fan

I’m concerned about the cooling- what are you doing to prevent condensation?

Also, I’d have the heat pump involved with DHW.

hot_rod

Skip the air vents on the distribution headers, the sep will do all the air elimination. An 1-1/4 Webstone purge ball valve right on the sep return cleans up that purge piping with one valve.

A fixed speed circ is fine for the indirect 15-58, etc. That pump will have a check, so skip the check on the one side of the DHW loop

30 lb relief only valve should be on the boiler, in the event it gets valved off. A second one on the system piping for the HP expansion.

There is a small glitch with HP for cooling and DHW. You'll get a short blast of hot water into the cooling mode. Noticeable with air handlers, probably not an issue with radiant cooling.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1809278#Comment_1809278

Yeah, unless there is zero latent load — a regular air conditioner produces zero condensation — you have to have some way to remove humidity.

Jimmie

I am not very concerned with humidity because it's rather dry here and I enjoy the humidity we do get. My cooling load (14k btu sensible) wouldn't be much because it also cools down 20 degrees here at night. It would just be to take the edge off the heat especially since I want to remodel my attic into a bedroom. I was thinking about just running the water temp at 60 or 65 degrees because I have been taking measurements this summer and we never got a dew point above that.

Thanks for the tips on cleaning up some of the purging parts.

I actually didn't know that a heat pump would be able to halt cooling and reverse for a DHW cycle.

Any ideas for how to pipe the heat pump to heat DWH in the summer? Would I just put some tees on the indirect tank inlets and run another pumped loop to the heat pump loop?

DCContrarian

I know the heat pump is labeled "future upgrade" but it's worth thinking about.

The way air to water heat pumps work is they try to measure the demand for heating (or cooling) and modulate the compressor and the water flow to match the demand. If the demand is less than the minimum modulation of the compressor then they cycle on and off.

I know it's tempting to limit the amount of glycol in the system but having the heat exchanger the way you have it makes it difficult for the heat pump to sense the heating and cooling loads. Heat pumps run at low temperatures compared to boilers, because their efficiency is highly dependent upon the temperature difference between the heat source and the output. By having a heat exchanger you lose a few degrees of temperature, which is going to cause an efficiency hit. Also, you have to have enough heat capacity attached to the heat pump to allow it to run at minimum modulation for the compressor's minimum run time. This is usually done with a buffer tank.

In terms of controlling when the heat pump runs and when the boiler runs, the simplest way is to have an outdoor thermostat that controls a relay that just switches the boiler on and the heat pump off below a setpoint temperature, and then reverses above a setpoint temperature. Because of the way heat pumps are controlled, in order to have a boiler "help" — supplement the output of the heat pump — the control logic of the heat pump would have to know about the boiler and control it. While there are heat pumps that will do that with a resistance heater I'm not aware of a heat pump that does that with a boiler.

DCContrarian

"Is it feasible to run my entire house as one zone and then fine tune the temps in bedrooms and sunroom with Caleffi Quicksetter balancing valves?"

Possibly, but probably not. The problem with balancing valves is that heat output of a hydronic circuit is highly non-linear to flow. And with a bunch of circuits in parallel like that on the same circulator, when you adjust the flow in one circuit it's going to change the system pressure and the flow in all the other circuits will change.

Any sort of fine tuning is going to depend upon the relative heating loads of the rooms being nearly constant. I notice one of the rooms is the "sunroom." Rooms like that typically have high heating loads at night and almost no heating load when the sun is out. If that's the case then simple balancing valves aren't going to give good comfort.

For what a Quicksetter costs, why not just have a thermostat and zone valve in each room?

Jimmie

I could probably zone my system room by room with a lot of math and complex controls, but since my house is so small it seems easier to just run everything as one zone and let heat naturally equalize throughout the space.

If I do add a heat pump, I am interested in a monobloc version to reduce installation complexity. I assume this would mean I need to run a 50/50 glycol mix to the outdoor unit since we get -30F winters. I do not however want to run the 50/50 glycol through the entire system because of the reduction in heating capacity. Would a heat pump not have wired temp sensors that could be affixed to the main piping for modulation?

I like the idea of an outdoor thermostat that alternates power between heat pump and boiler. What would this device be called and where could I get it?

DCContrarian

"I could probably zone my system room by room with a lot of math and complex controls, but since my house is so small it seems easier to just run everything as one zone and let heat naturally equalize throughout the space."

No math. Just a thermostat and zone valve in each room. The zone valve has an end switch that closes when the valve opens. Run all the end switches in parallel and have them control the circulator pump, so if any zone is open the circulator runs. That's it. At a bare minimum it's like $10 for a thermostat and $45 for a zone valve per zone, a lot cheaper than a Quicksetter.

DCContrarian

"If I do add a heat pump, I am interested in a monobloc version to reduce installation complexity. I assume this would mean I need to run a 50/50 glycol mix to the outdoor unit since we get -30F winters. I do not however want to run the 50/50 glycol through the entire system because of the reduction in heating capacity. Would a heat pump not have wired temp sensors that could be affixed to the main piping for modulation?"

In order to sense the heating load the heat pump measures both the flow and the temperature drop. (Heat flow in BTU/hr equals temperature drop in F times water flow in GPM times 500). It can measure the flow through itself, but it can't measure the flow on the other side of a heat exchanger. For the most part they don't have any sensors at all in the house, they're almost passive devices. They read the return water temperature and adjust the flow to try and keep the temperature drop constant, then adjust the compressor to meet the load.

hot_rod

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a good heat load and system deign would tell you what gpm each loop needs at demand condition . With an ECM delta P circ as you show it is best to use a dynamic balance valve, caleffi 137 as an example

With the HP outside, either glycol or an I-stop freeze valve is need in cold climates

You can size plate heat exchangers with a “close approach” method, where the A &B sides run within 2 degrees of one another. Most of the plate HX software give you that design option.