Posted by: @derek-m

↑

Alternatively you could buy a very large quantity of clean, dry, air (preferably warm) and use this as the air supply for your heat pump. 😋 

Do you mean like this?

A bit Heath Robinson but maybe some clever person could design something more bespoke and market it to ASHP manufacturers. 

I love it. A perpetual motion machine.

Mike

Posted by: @sentinam

↑

Posted by: @derek-m

↑

Alternatively you could buy a very large quantity of clean, dry, air (preferably warm) and use this as the air supply for your heat pump. 😋 

Do you mean like this?

A bit Heath Robinson but maybe some clever person could design something more bespoke and market it to ASHP manufacturers. 

 

 

So instead of using the water to take the thermal energy out of the home, he uses the air. I wonder how effective it is in practice.

One possible way to keep the heating operating during defrost cycles could be to use a large heat store.

An alternative would be to have a small heat pump to provide the energy required for defrosting.

Whatever method is used, it will probably still use more energy.

Now it’s just done a frost cycle at 3.5 degrees outside and not a bit of frost to be seen. Heavens to Murgatroyd!

The Grant units seem particularly keen to defrost around every 45 minutes when there's high relative humidity and the evaporator refrigerant temperature is below freezing point. It's an issue prevalent in the UK with our mild but damper winters, air at -10degC 100% RH has less than half the moisture content of air at 0degC 100% RH. That's why Scandinavian climates suit ASHPs really well. Commercial cold store evaporator coils have much wider fin pitch designed to accommodate ice build up, and hot gas defrost, but that would make domestic ASHPs rather unwieldly and large. Not much you can do practically speaking. You just need to remind yourself that for the remainder of the year save those two or three winter weeks when the kWh consumption rockets you've got a very efficient heat source. Ebac has launched a UK designed and made ASHP claimed to perform better in the UK winter than many imported brands. https://www.ebac.com/air-source-heat-pump

@allyfish that totally fair enough Ally,makes sense. 
the problem with the defrosts though right now is getting the house to temperature when the LWT won’t go above 36 and heating is turned off ever 45 minutes and needs to build back up again.

@mab As it's been seconds since any graphs were posted, here are two interesting ones from over the weekend, both showing a couple of defrost periods. I've changed my monitoring to record every minute. and this does show something interesting (well, it takes all sorts) but predicted(?), that the defrost happens differently (better?) at lower temperatures.

This first one is when the OAT was around -7. The Discharge temp (assume that's the temp coming from the refrigerant as it's higher than LWT) maintains a steady temperature, and then drops down when the flow/return temps swap to do the defrost, as expected. Note how the Defrost temp is fairly constant around -10, and the LWT stays level or increases slightly until the defrost happens.

But on this second night, the OAT was hovering around zero, and this seemed to drag down the defrost temp a lot more, which then pulled down the Discharge temp with it, and consequently the LWT plateaued then dropped before the defrost process even began.

This confirms what you mentioned a couple of days ago, that performance at lower OAT (once the HP goes into the deadly defrost cycle loop) is actually better - or at least not as detrimental to the LWT.

OAT now is around 3C and thankfully defrosts are more every 90 mins. Yay. 

I decided to stop fretting and tinkering and watching the LWT just leave the new WC settings and see what happened. Lo and behold the radiators are hot and the place is heating up. 

I think having the temp for the minim outdoor temp to max LWT at zero will help for future. Installers had left it at -4.

Same here @Marvinator80. I have max LWT (in my case 45degC) set to 0degC. To be fair below 0degC I don't reach max LWT, due to continual defrost cycles and the unit running flat out in between try to raise LWT after each plunge. Last weekend I had the ASHP & heating on 24/7. Usually I switch it off between 9pm and 5am. That was to keep some heat in the circuit overnight in very low temperatures. In more typical winter weather such as this week I revert to switching off, it pre-heats up reasonably quickly.

As an experiment I tried disabling WC and reverting to max system heating temp of 50degC as target LWT, Made knack all difference as the Aerona was too busy defrosting itself to get anywhere near 50degC! Also, the house heat loss was high so the RWT was quite low. My 10kW unit is borderline sizing, I was originally looking at 13kW but ran into DNO issues with notification approval and rating of my 80A main fuse, so we dropped to 10kW which is connect and notify. The log burner provides secondary heating if the system struggles to keep temperature, which it did last weekend.

@allyfish makes sense Ally. Feels good that we are making progress. Thanks for all your help.

the gap between my LWT and return is typically 5 degrees so is that decent?

Another thing I did that helped last night I think was completely turning off the heating to the room above my garage. This was an additional build in the summer and I think the extra 3 rads probably weren’t helping. 

13KW pump for 294sqm with low heat loss was fine after it was installed last year so I think this new garage room (48sqm)has made a difference. The water has to travel further and out of the house underground to reach it too. 

I’ll probably put an as efficient as possible fancy WiFi electric radiator up here and programme that to heat the place up in the mornings and use the plumbed radiators on a low setting as background heat.

10 degrees when I went into my mancave this morning at 8. An old electric heater has it up at 18 now. 

We are the same as well, log burner means that if needed a quarter of the house can be heated by that and the UFC click off so I guess more can be targeted elsewhere.

@mikefl your data collection is rather better than mine 🙂 . I ought look into systems for reading data - are you reading it from the aerona somehow?

I think we are getting closer to understanding the aerona defrost (but i still don't know how it decides to do a defrost if its >40mins since the last one as mine still are coming at 40mins when I'm home to watch it.

Actually i think my WC is set at -4c - I'll try changing that to 0c when i get home...