Condenser in lounge room floor

[LeighC]

Hello to all the experts out there,
I am designing a new lounge room area over a raised subfloor, it maybe a sheet of aluminium or steel over an insulated base.
My question is could I use a heat pump & pump super heated refrigerant directly into a circuit welded or clamped to the under side of the sheet floor to warm it during the winter similar to a warm condenser?
Would this work without the need for a glycol circuit & circulation pump?
Pardon me for my ignorance, my qualifications mainly only relate to vehicle A/C systems
My winter ambient temps only get down to about 0° C but I would like a warm floor.
Thanks in advance - Leigh

[seanf]

Would using a glycol circuit not make the initial design easier, and if the refrigerant type used had to be changed in the future then atleast if refrigerant pipework changes had to be made you wouldnt have to lift the floor. Also keeps any hazards of the refrigerant outside.

[r.bartlett]

The condensing temperature at outlet would be far too high over 70c. then it would cool to condense to room temp.
therefore you'd have a really hot part of the floor and a cool area. use it as it was designed or get a air/water system,

[LeighC]

Thanks for your replies, yes I thought this may be the case, I had the idea of using a fairly thick sheet of aluminium say 10 mm it would work as a heat sink and disperse the heat a fair bit, but it would be defeating the purpose if you cooked your foot in one place & cool at the end, maybe using standoffs from the coil to the plate on the 1st say 30% & gradually get closer to the plate as it progressed to the end. The subflloor would be highly insulated with say 75 mm of PIR spray foam. I was just trying to avoid another glycol cooling loop & pump & servicing as in a normal hydronic floor setup with a heat pump. Does an indoor air to air split system get warmer at one end of the coil in heating mode or is it designed to stop this?
Thanks - Leigh

[nike123]

No matter what is type, all direct expansion/condensation type of heat pumps, at one end of condenser you have superheated vapor of about 70˚C and at another end subcooled liquid of about 35˚C. When radiant floor heating is designed, we use 5˚ ΔT of heating liquid and max temperature of return water of 35˚C because of health issue with high floor temperature (and heat related expansion of materials). Therefore, your idea is not feasible.

[Tayters]

Does an indoor air to air split system get warmer at one end of the coil in heating mode or is it designed to stop this?
Thanks - Leigh

If I remember correctly from what I was taught in fridge school the central 70-80% of the coil is where the refrigerant is changing state. In the condensor this is roughly 40°C, could be more or less depending on application and conditions. Superheated gas on entry and subcoooled after.
By design the coil will be hotter going in and cooler going out, this will be quite noticeable.

In an AC unit just need the air passing and all good. The coil pipes do zig zag about the place to some extent.

If heating liquid then a contraflow system is used. This means water flows opposite way to refrigerant - water out meets the hotter refrigerant in. Suck more heat out of the refrigerant that way.

The only water systems I work on are pool heaters and you don't see more than 1°C difference between water in the heat exchanger and water out.

Cheers,
Andy.

[LeighC]

Thanks for all your great explanations, I have learnt enough to rethink this type of floor heating & we may as well close this discussion.
My Reno is getting done as close as I can to Passive House standards with a MHRV system & I am investigating a Genvex HPV series & will still try & get a warm floor.
I am trying to find an agent in Australia at the moment.
Cheers all & keep safe - Leigh

[nike123]

Passive House mean you dont need heating at all. Underfloor heating is usualy about 100W/m2. Pasive house heat demand is below 10W/m2.
You only need heating of fresh air, if at all! Therefore, you should consider installing heat recovery system for fresh air!

https://www.heliosventilatoren.de/en/product-range/ventilation-with-heat-recovery

Or, somebody is selling you Pasive House fairytale!

[LeighC]

I was in a passive house a while back with a raised timber floor that was insulated with batts (similar to mine) & my feet were still cold but the room itself was OK & it had a Zhender Q 350 heat recovery system installed, seems its got something to do with the hot air rising. We get about -6°C with many severe frosts in a row in winter, & we are getting older & appreciate more comfort. I am going to install a heat recovery system of some sorts. Thanks

[kiwifridgie]

There are electric underfloor heating"tapes" that are laid over the floor and under the carpet. - best way long term.
A glycol/ water circuit in a false floor slab (lay pipes over floor, cover with levelling compound/screed) would be next best.
Condenser piping might work, but not easily and expansion/contraction would ruin any perfection you ever achieved. Just no.