Adding cooling to in-floor radiant

fgamache

After the recent years' heat waves in the Pacific Northwest I am looking to add some cooling to our house.

Favourite option so far is air-to-water heat pump and making use of our in-floor radiant loops.

Curious to better understand why I would need a buffer tank between the heat pump and the primary loop. I mean, the propane boiler doesn't need/use one? Why can't I just hook up the heat pump supply & return to the primary loop directly? Doesn't seem to be an operating pressure issue like if I was using a geothermal heat pump...

pecmsg

You need to control the relative humidity before cooling the floor. 

Easiest solution is a few mini splits

PRR

> Adding cooling to in-floor radiant
Is that even a thing?? In my humid clime, I'd get wet floors. (As pecmsg says.)
If I let my main-floor air fall to the 55 degree cellar floor, it's stinky-damp down there.

I think you need 'gutters' under your heat/cooling coils. Like the "A-coil" in the A/C add-on to my hot-air system. And it drips a very significant amount. And retrofitting 'gutters' to a floor seems absurd? (Perhaps an invention that is not yet ripe?)

Hot_water_fan

Start with Caleffi’s Idronics series! There’s one about air to water heat pumps. If you’re using a slab, a buffer is probably unnecessary. 

fgamache

PRR said:

Adding cooling to in-floor radiant
Is that even a thing?? In my humid clime, I'd get wet floors. (As pecmsg says.)
If I let my main-floor air fall to the 55 degree cellar floor, it's stinky-damp down there.

We are very humid in winter but summer is bone-dry here and the dew point in my area only reaches above 15ºC (60F) only on exceptionally rare occasions; I can't imagine I'd ever want the floors that cold. Just looking to 'take the edge off' for maybe a week or two during peak summer heat waves; I'd be thrilled to keep the slabs below 25ºC on those occasions. Rest of the season is lovely and needs nothing more than open windows!

fgamache

pecmsg said:

You need to control the relative humidity before cooling the floor. 

Easiest solution is a few mini splits

Yeah, not interested in mini splits for esthetic reasons. Like in my other comment, humidity is not an issue where I am...

Hot_water_fan

The Idronics will show you how to do this. The issue isn’t only the outdoor humidity though- people, the things people do, the pets they have, etc all can raise indoor humidity higher than outdoor. 

DCContrarian

fgamache said:

Curious to better understand why I would need a buffer tank between the heat pump and the primary loop. I mean, the propane boiler doesn't need/use one? Why can't I just hook up the heat pump supply & return to the primary loop directly?

It has to do with the way heat pumps run and are controlled. Heat pumps work best when they run continuously at a constant output and if they have a modulating compressor they can match the compressor speed to the load and run continuously. An air-to-water heat pump will have a variable speed compressor and variable speed circulator, and the control electronics will try to modulate both the compressor speed and the circulator speed so that the water leaves at a fixed temperature and returns at a fixed temperature. If the return temperature starts dropping it will turn up the compressor to produce more output, and turn up the flow to maintain the temperature differential.

If the return temperature starts rising it slows the compressor, until it gets to the minimum modulation, maybe 25% of output, at which point it starts cycling the compressor on and off. The circulator keeps running, so that the compressor can tell when it's time to cycle back on again.

On the inside of the house, thermostats turn zone valves on and off to regulate the temperature. Since the circulator has to run all the time, there has to be some place for water to run when all the zones are off. That's what the buffer tank is for. Compressors typically have a minimum run time, the buffer tank also serves to soak up capacity and prevent short-cycling.

It's not conceptually that different from the way boilers work, where thermostats control the zone valves but it's the aquastat and the water temperature in the boiler that controls whether the boiler fires. Boilers typically hold enough water that they effectively act as their own buffer tank.

pecmsg

Having a 45* floor is going to be uncomfortable. Any thing higher and it won’t cool the air space. 

Zman

I think that the buffer is required to keep the heap pump from self destructing from short cycling.
This is very informative.https://www.youtube.com/watch?v=CVXGMuB8wlU

hot_rod

I think HBX offers a stat with a dewpoint sensor. That is how you want to control radiant cooling. The chilled floors can handle some of the load, in arid climates, perhaps all. So first you need to find out what the cooling load is for the home. a cooling load calc.

Then determine what the floor is capable of providing. In arid climates you could get by with just radiant cooling.

It's all in the numbers. The math gets a bit involved for slab cooling. Rehau, Uponor, others have design guides for radiant cooling.

A buffer can also help when a2whp go in to defrost. It pulls heat back from the buffer instead of using resistence heat. So you defrost with buffer water that was generated with 2 or more COP