Add air to water heat pump to radiant heating system
Hi, I am looking for advise on ho
w to add a air to water heat pump to my radiant floor heating system running on a propane boiler. Buffer tank that was sent is 2 port. Anyone has any advise in how to pipe it all up? Here is design I got do far.
Comments
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If you have a tank with enough connections a 3 pipe buffer gives you a bit more efficiency. We talk about it in this Idronics issue
Consider a plate HX between the HP indoor module and the buffer. So you don't have to glycol the entire system.
Your 2 pipe drawing is correct if you go that route, still consider the HX.
I downloaded the SWEP HX sizer software. Alicia and Nathan at SWEP walked me through a couple sizing examples, on a phone call.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
My buffer tank onky has 2 port. Thaught was ordering a 4 port but ended up getting a 2 port.
Also, i should have mentionned, the whole system is running water. Heat pump is a split system so refrigerant is running from outside to the indoor unit ( prettymuch is a refrigerant to water plate echange). Then circulating water to buffer tank from there.
I am understandibg there are concerns with 2 port buffer tanks that cold water may try to run trough unused boilers, and adding check valve may offer resistance and prevent that.
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2 pipe works fine. You show checks on both sides of the boiler. The circulator may have a check? Add a spring check on the other side.
A pressure gauge on tank, maybe an additional 30 lb relief valve also, in case the boiler gets valved off. Maybe the HP IDU has a relief inside?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
I do not believe that heat pump as relief valve, this would be added anywhere in the heat pump loop? The gas boiler does have a 30 lbs relief valve already.
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My HP came with a tee and relief valve to be installed on the job.
You want to make sure there is a relief to protect all the components should one of them be valved off.
If the boiler ever got valved off, and the only relief is on the boiler, the HP and tank are not protected.
With that 53 gallon buffer and all the piping, make sure to run the expansion tank sizer program. Amtrol and Wessel have free sizers at their websites.
Or long hand calc with the Amtrol Engineering Handbook :)
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
The question is, who's in control?
What's more important than how it's plumbed is how it's controlled. Do you want to be able to switch between the two systems, with only one ever running at a time, or do you want to be able to have them "help" each other out?
If it's the second, the heat pump has to be in control. Any heat pump worth installing has a variable speed compressor that modulates to meet the load. If there is also a propane boiler in there that it's not controlling it's not going to be able to sense the load, and as soon as the propane kicks on it's going to shut off.
Heat pumps that can control a boiler are rare. There was discussion of one here fairly recently, I think it was sold by US Boiler.
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Plan for controll is heat pump has option to controll a electric backup, sending 240V. This will be feeding a relay controlling the heat pump. That is plan A. Plan B is if this does not work, all controls will go into a hbc eco-0600. It is design to controll staging of and bavkup switching between multiple heat pumps or boilers.
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Your drawing shows an external pump. There is no pump inside the unit? You generally want a speed controlled pump with these, if not built in, they usually have a 0-10v or PWM output for controlling one. You can use the + variant of these as it has 0-10v control:
Heat pumps are similar to mod cons as efficiency is all about temperature except with a heat pumps the efficiency hit is much larger (order 20% to 50%). You always want it to supply the coldest water your place needs and you are never mixing down the supply water with any return, so make sure you don't overpump the emitters. Outdoor reset is your friend, set up properly.
You can also get a bit of efficiency boost if those zones valves can be set to bypass flow when closed. This way some heat will always be provided to all zones but you still have control over temperature.
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So, for the relief valve, should we just connect one on say, thr cold water return at the buffer tank where all systems would be protected?.
And heat pump has a 240V output relay to controll a pump. Pwm provided on my unit
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yes a relief on the buffer protects whatever device is hydraulically connected.
The boiler generally have a factory supplied relief. Sometimes it is installed, sometimes the fittings are in the box. Install that one as the manual shows. That is your warranty protection as well as a code required safety
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Find out what the PWM signal is. Most 0..10V is fine with either 10V or 12V PWM, you can also put a simple RC filter on the PWM output to turn it into an analog signal. If the 0..10 is not an option, you might be able to get close enough control by tweaking a delta T circulator.
I used an RIB relay with a 240V coil to drive a 120V pump.
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Using the 220V out from the heat pump to control a boiler might work. The only thing I would worry about is short-cycling, the heat pump is expecting the device it's controlling to be an electrical resistance element that doesn't care how long it's on for. This is basically how heat pumps that have a boiler control work, except they're aware that the thing they're controlling is a boiler.
A multi-stage thermostat is going to give issues. Think about how a boiler is normally controlled. The thermostat turns the circulator and/or zone valves on and off. The aquastat in the boiler is set to hold a certain temperature, when it needs to it fires on and off. The thermostat isn't controlling whether the boiler fires. Air to water heat pumps operate similarly to boilers, the thermostat doesn't control the heat pump, it controls the valves and circulator. The heat pump looks at the temperature of the returning water to decide whether to run. Any heat pump worth installing is going to have an additional wrinkle, where it modulates to meet the load, so it's going to be looking at the flow and return temperature to try and estimate the load and meet it. If you throw in a boiler on the same circuit that the heat pump doesn't know about it's going to mis-estimate the load, it's going to think it's a lot lower than it really is and reduce its output. When the return water doesn't get much colder it's going to reduce further, until it shuts off.
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What is the make & model of the heat pump?
Luke Stodola0 -
it is a chinese from alibaba. "Fantastic" FE IHCDO8OSS
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It would be helpful to get the I&O manuals
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
This os fhe wiring schematic
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you do have an electric heat relay connection. A manual that explains the operation would be helpful
Luckily you have a reactor on the upper left side🤓
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
My AWHP toggles the aux heat relay a fair bit when enabled. Not something I would use to kick in the boiler.
Your boiler might have the option of a remote sensor. If you can install this on the top port of the buffer tank and set the boiler to have an ODR curve that is a bit bellow the heat pump (ie boiler targets 35C when AWHP targets 40C). This way the boiler would only kick in when the heat pump can't keep up.
Overall, I think the simplest option is to manually select between the two.
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I know, i will only figure out once I power it up I guess. The mnual sqys nothing about the backup configuration. Like I said before thats plqn A. But if I dont like how it handles it, plan B is a 3rd party controller for both.
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There isn't a third-party controller that will control both. Air-to-water heat pumps aren't controlled like air-to-air heat pumps.
Kaos' idea of using outdoor reset it interesting. If you have two boiler-type devices on the same circuit, the one with the higher aquastat setting will always fire first, the other one will only fire if the first one can't meet the load. If both devices have outdoor reset, but their curves have different steepness, you could set it up so the heat pump has a higher setting when it's warm out and the boiler has a higher setting when it's cold.
But that's a lot of work and may not work as intended.
I guess the question is, what are you trying to do? Is it:
- Use the boiler instead of the heat pump at temperatures when the boiler fuel is cheaper than electricity?
- Use the boiler to supplement the heat pump at temperatures when the heat pump lacks capacity to meet the heating load?
- Use the boiler to boost the water temperature at outdoor temperatures when the indoor radiation lacks the capacity to meet the heating load at the water temperature the heat pump is capable of providing?
- Use the boiler as a backup in case the heat pump is unavailable?
Each of those would require a different control strategy.
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