Anti-freeze valves required?

[AndySat]

Just took delivery of the ASHP for our new build. It's the 4kW Haier R290 (the same unit as @JohnMo has) and initial impressions are good - it seems well made and it's certainly a hefty item...

Sadly, Wolseley no longer include the wiring centre, so that's another £500 to spend, which makes it less of a bargain. I don't understand why the wiring centre isn't included, 'cos the ASHP is useless without it.

 

I'm collecting the plumbing bits to get it installed and was planning to get two anti-freeze valves, but then I read that they may not work unless they're fitted at the lowest point in the pipework. In my install, the pipes go down into a duct under the floor slab and resurface in the plant room, creating a trap that can't be drained. Is there any point in fitting anti-freeze valves in this case? They would still drain the ASHP itself, which is probably the important thing.

 

My install looks something like this:

 

[SimonD]

Anti freeze valves are as you've assumed, to drain the heat pump and avoid damage there. You might want to double check the installation manual as some manufacturers are starting to allow installations without them. You don't need to worry about draining the rest of the system sitting inside the heated envelope.

[sharpener]

Unless you are massively confident you will never get a prolonged power cut while you are on a winter holiday in the Canaries you should either use an antifreeze additive (glycol of some kind, they are not all the same) or fit AF valves. Inta are reputed to be good, others variable. Pipes inside the building/slab are less likely to freeze than the HX in the HP.

[JohnMo]

That's a shame about the wiring centre, mine was in the box.

 

Not sure how thick you screed is but I ran into issues with the heat pump hunting. We have 100mm screed and wide pipe spacing (300mm) and found the heat pump wasn't getting the response it expected from the return temperature and it would hunt (power and temperature would yoyo) killing CoP.  I have full monitoring and you would have noticed the hunting otherwise as it's not that easy to notice.  But it knocks 1.5 off the CoP.

 

I have since hydraulically separated. So have a primary loop around 6 to 8m long, with close coupled tees.  The secondary side has its own pump. I then run it at fixed speed on the primary and secondary side, with secondary side slightly lower flow rate.  This gives the heat pump some feed back - so far in cooling it's been great. Also the pumping power dropped with the second pump as both were doing less work individually and maybe at a better efficiency point.

 

I also don't bother doing cylinder heating with heat pump. Logic for me, I have plenty of solar, but also I can leave the heat pump to run long and slow heating the floor. Time of use tariff make it cheap enough even without solar.

 

If you any questions just ask.

 

Believe your warranty requires either anti freeze valves or glycol.  Glycol is the work of the devil, so go that route.  The antifreeze valve is only to protect the heat pump. I have isolation valve on the screwed connectors on the heat pump and then the antifreeze valves. What you pipe does after that doesn't matter the heat pump is protected.

Edited 7 hours ago by JohnMo

[AndySat]

Thanks everyone.

 

Yes, I should've read the manual! It says that, to avoid damage in freezing weather in the event of a power cut, either glycol or freeze protection valves must be used. I don't want to use glycol, so I'll get some anti-freeze valves, even if it's just for peace of mind.

 

4 minutes ago, JohnMo said:

Not sure how thick you screed is but I ran into issues with the heat pump hunting.

 

Screed is 55mm cemfloor from memory, over 170mm of insulation. Pipes are mostly at 200mm centres, a bit tighter in the bathrooms where there isn't space for a lot of pipe. Floors will be tiled over a decoupling membrane. ASHP will be doing hot water as well as UFH.

I'll have some basic flow/return temp monitoring in place, but nothing sophisticated, at least not at first. The plan is to run with simple WC and keep the flow temp as low as practical, with the option to throttle the shorter loops at the manifold if those rooms are getting too hot.

I'm expecting the first winter to be a learning experience, as ASHP, UFH and MVHR are all new to me, so no doubt some tweaking and tuning will be needed. As long as we don't need to sit indoors in thick coats, we should be fine!

 

I'm sure there will be more questions to follow once I get into the install...