Control suggestions please

Rich L.

Hi Wayne, Here's a link to the Takmar 256 install and setup instructions.

http://www.tekmarcontrols.com/literature/acrobat/d256.pdf

If you went this route WW, you would be controlling the heat pump off the boiler contacts in the 256 based on the water remp in a buffer tank. I'm not sure how familiar you are with heat pumps so sorry if you already know all this but you really need to use a buffer tank with a heat pump to prevent short cycling. Rule of thumb is a minimum of 10 gallons per ton of capacity up to 5 tons/50 gallons. I like using electric water heaters for the buffer. You would place the system temp sensor for the Tekmar on the line leaving the buffer tank going to the heat pump. This way the Tekmar is controling the tank temp based on outdoor temps. The Tekmar boiler contacts go to the heating side of the heat pump. I like to zone with zone valves and like to use Taco ZC controller. You can have the stats go to the Taco ZC, and a call for the boiler goes from here to the Tekmar. Then the Tekmar decides if it needs to call on the HP or not. Hope this doesn't sound too confusing, it's really not.

I attached a crude drawing, I don't have any nice drawing software (or know how to use it!) NOTE: I did leave out isolation valves, exp tank, air elimination , etc. Just trying to show the basics.

The one other issue you avoid with ODR is the flywheel effect in milder temps. A gybcrete system is a higher mass system and with lower temps of ODR can help you avoid overshoot in the shoulder seasons.

Good luck WW, Rich L

Wayco Wayne_2

I'm helping a friend

who is doing a radiant floor job. He has a ground source heat pump feeding a buffer tank which is then feeding 3 zones of radiant floor. The radiant floors are gypcrete overpours. He is thinking of using outdoor re-set on the water leaving the tank. Would the newer Tek mar control work here or is that overkill? Any suggestions from those with experience is appreciated.

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Wayco Wayne_2

Here's a

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"quick diagram of what I'm picturing. WW

Unknown

Just,,,

ofF the top o' my head. I think I'd set the tank for as low as it can go and still keep the place comfortable on the coldest night with continuous circulation and then control each floor pump with a slab/room sensing Tekmar t'stat. Sorry, I don't have the model # available right now. I do kind of think reset on the tank might be overkill.

Wayco Wayne_2

Thanks

I like the simplicity of it. The idea of using reset was to possibly reduce any striping that may occer. Any comments on that? WW

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Dave Holdorf_2

Water Temps

Wayne-

That depends on the design water temperature needed.

If it is low, say in the 90-100 range than the window of reset water is very small. Lowest water temperature I like to circulate through a radiant floor is 15 degrees above thermostat setpoint.....70 thermostat setting, 85 degree water temp.

Now if your system needs a higher water temp close to the heat pump output of around 120, then I would do some reset. You now have a 35 degree range to work with.

When considering the piping, treat the buffer (storage) tank like a boiler......now do your mixing strategy. For this application I would use a mixing valve with outdoor reset rather than injection. Low heat source water temp, low radiant temp and you will get a full range of operation of the mixing valve. An injection pump is not going to work its magic of Delta T like when you have a high temp boiler to work with.

Rich L.

Mixing?

Unless you need different temps for different areas of the home there's no need to mix. That's part of the beauty of the heat pump. A side benefit is the lower the temps your looking for the higher the efficiency of the unit. For that reason I use a Tekmar 256 reset controller on my HP system. As far as thermal striping goes that's going to be dictated by the tube spacing, not the water temps. BTW the tube spacing on a gybcrete job is critical, ask me how I know, just don't ask my wife.

I assume you're cooling with it too? Fan coil or radiant floors? If fan coil I have a really cool control that monitors outdoor temp and at a set temp (mines at 45*) sends HW to the fan coil instead of the floor on a call for heat. Works great for the shoulder seasons to avoid the flywheel affect of the higher mass of gybcrete. It's an interface between the thermostat and the HP.

First year in the house (last winter) I set it up like MPF suggested and it will work but you wind up with cool floors most of the time when not at design temps. The HP also has to work a lot harder to maintain the higher temps.

Wayco Wayne_2

My friend

tells me he is installing a heat pump that has DX for cooling and water to water for heating all in one piece of equipment. Sounds cool to me. I'm more of a boiler guy, and don't kknow much about cutting edge geo thermal HP's. All zones are the same temp. 105 at design. I'm inclined to think at that temp we don't need any reset. Just good t/stats with anticipators set for radiant floors. I love the feedback. Thank you very much.

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Rich L.

Reset

"All zones are the same temp. 105 at design. I'm inclined to think at that temp we don't need any reset."

Wayne, There's no question you can do it without reset and your friend will have a comfortable house. My point is that there will be the vast majority of the time you won't be at design and you could be saving more and have greater comfort. The huge factor with radiant floors is people (unrealistically) think they're always going to be warm. We as heating contractors know that's not the case and that the only time they're going to be warm is when the house, or room, is calling for heat. With outdoor reset we can make that call be much more often and therefor greatly increase that comfort level. (personal experience again!)

Adding reset to a geo system is a little like using a mod-con boiler. Sure we could put in a cast iron one that's going to take care of those cold snowy nights when it's -10 out. But what about all those other nights when it's 20 above? The lower the supply temps, the cheaper to operate. A little more investment now saves him money, and gains comfort, over the life of the equipment.

If you don't do it I can already hear your friend asking why his radiant floors aren't warm all the time. Educate him ahead of time if you don't do reset to save yourself the grief!

Good luck, Rich L

Wayco Wayne_2

Rich...

If I hear you correctly you are saying that since a system without reset will heat up the slab and then turn off and coast with the heat off that there will be less comfort floor temp wise, than if we use reset and have longer cycles, thus having less down/coasting time? If I were to use a Tekmar 256 rest control. Where do I put the sensor and what do I control? The heat Pump operation? Thanks again for your input. WW

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