A2A Heat Pump minimum working temperature?

[Ferdinand]

Here's a piccie of my temporary setup using the AirFlex15.

 

The insulated duct is quite chunky. t the extent that a more perma-solution is not imo acceptable looking like that in my kitchen. I would either want it done as a real outlet hidden behind the unit going through the wall. In that case I think I am better with a real A2A one (inside or outside unit) and a 70mm connector.

 

 

 

[Gill]

On 29/11/2023 at 12:32, Ferdinand said:

 

The insulated duct is quite chunky.

 

Thanks- really useful to get a visual on it.  I'll be keeping it in the back of my mind for summer if my garage conversion gets toasty.   

[HughF]

This is after 20 mins running this morning….

[Gill]

On 02/12/2023 at 08:19, HughF said:

This is after 20 mins running this morning….

Is that frozen? Looks like candy floss but I'm assuming it's not. 

[Gill]

On 27/11/2023 at 10:57, Ferdinand said:

So there is cause for caution at lower temperatures,. and probably a need for some sort of Plan B.

 

Mine 'defrosts' - or I assume it is defrosting when it stops and starts draining water into the bucket on the drainage pipe - from time to time.

 

After a week of low temps and high humidity, some observations. 

 

Defrost cycles have increased. I've yet to spot one taking longer than 5 mins and more than two an hour. We we've been below 0 for a few days now (-2 consistent day temps). Energy use has spiked at a max 66kWh on the coldest day. Comparing to last years usage we were 85kWh over heavy cold spells and outside of that averaging daily winter use around 55.

 

The living room unit is being over worked and takes time to get the room to temp. That was my downsizing in advance of heat loss improvement. Belive that is causing more defrost cycles. Still comfortable eventually and running constantly to avoid the room getting below 14 overnight seems to be working better. 

 

Our bedroom unit is on a separate outdoor unit. That room opens into our living area and having both units running seems optimal for warm air circulation. If I ever wanted to add another unit to our living area, I'd connect it to the outdoor unit that runs the bedrooms - that way it's unlikely to be on same defrost cycle. 

 

Overall happy with the last weeks 1st real performance test. 

[Ferdinand]

On 30/11/2023 at 20:33, Gill said:

 

Thanks- really useful to get a visual on it.  I'll be keeping it in the back of my mind for summer if my garage conversion gets toasty.   

 

It's notable to me how much difference each progressive step makes, since I developed it slowly due to my serious illness.

I'd suggest making a point of doing all three:

 

1 - Insulated duct *not* uninsulated duct (leaving it uninsulated creates a duct-surface-area-inside-the-room radiator working against your heating or cooling goal). My 3m one cost about £35.

 

2 - As good a baffle in the window opening as you can make. The one that came with my unit was suitable for windows with an obtangular opening (eg sashes), but sized for an uninsulated pipe. I started with cardboard and eventually made one from plywood.

 

The gap around the edge is less of a hit than might be expected - at an average 3mm gap around a 150mm pipe with 25mm insulation it would be leaking area/inlet area = (2*PI*100mm*3mm)/(PI*75mm*75mm) as a fraction, which I make 0.05.

Not zero, but fairly marginal.

 

(That calc ignores edge leakage around the baffle and temperature variability effects between where the baffle is located and where the end of the pipe is located.)

 

For cutting the leakage I would use a bit of rockwool or material round the pipe, and probably sticky foam strip around the window frame.

 

3 - Sort out your water drainage outlet - I use a watering can and a piece of beer-making-type hose with the end cut at an angle to concentrate any flow, which was easier to manage/cut tidily than hose pipe.

 

HTH

 

F

[Ferdinand]

On 03/12/2023 at 22:51, Gill said:

 

After a week of low temps and high humidity, some observations. 

 

 

 

For a comparison, these are how my usage has worked out recently.

 

Factors are:

- It is Gas for heating, nearly all hot water (one electric shower), and cooking.

- The A2A heat pump as described. CoP about 2->2.5, so puts out 2.5->3kw for 1>1.5kW of input.

- I have a new air-fryer cooker which I have been using quite extensively -> transfer from some wok cookery on the gas, but also from the Electric Oven.

- I have a solar array put in in 2016 which reduced my annual electricity consumption by something like 30-35% like for like (finger in the air estimate). If I go for more electrical heating that will work the other way.

- Living on my own in a largish 4 bed house (200 sqm approx). 

 

Usage numbers.

- During the summer I was using about 4-5kWh of imported electricity per day. Figure from smart meter.

- When I got the air fryer in, and started dabbling with the ASHP in heating mode during Oct, that went up to around 7-8kWh per day.

- During the current cols snap that has jumped to around 10kWh per day. I hope to keep it at that level as a max.

- Gas use during the summer was cooking / water, so very little.

- Since early Nov I have been running a bathroom radiator a couple of hours AM and PM. Put usage up to about 1-1.5  cubic m per day (which I make ~15 kWh).
- My downstairs heating controller was replaced in mid-Nov, and I have that on driving the UFH over the downstairs to provide some baseload heating. That has put usage to about 4 cubic m per day, which I make around 44 kwh.

- For an early morning boost I have occasionally been using the wok ring for 15 minutes whilst cooking breakfast, which is not quite optimal efficiency or C02 wise, but a good instant boost.
- Bills for 4 Nov -> 3 Dec were £60 gas and £70 elec. I think I need to get to grips with the the new GFCH controller to use gas more efficiently by setting up daily timings rather than default, judging by the weekly gas usage where 45% of the last 4 weeks was in the last week, or it could run away with me like last year. 

- TBF, my current regime is a little hair-shirty, back to the old "warm certain rooms" method (baths + kitchen-diner), and the rest running .. er .. 'cool' ! House is OK-good, rather than near-passive.

 

Graphs

 

Reflections

 

- Last year I was caught out a little by the amount of gas I used for heating, which having done a retrospective audit of bills recently was more than I thought it was. But I was incapacitated by illness.

- This year my stretch goal is to keep bills below £100 per month except for Nov / Dec / Jan / Feb (say £800-£1000 total for 12 months), and to break even when solar exports and FIT are added in. That is a bit of a stretch goal TBH, especially on the heating side.

- Further improvement will depend on the supply side and a switch to electric heating, so likely more solar / solar export and a house battery. Not much scope for improving fabric performance since it was all done just before we bought it around 2008 - except perhaps draughts and drylining as I need to redecorate certain areas. A detailed heat model analysis may help.