Air Source Heat Pumps

Swipe

Just a quick question regarding power consumption/efficiency of using my two Daikin inverter heat pumps. Is it more efficient i.e. less power input required to run the indoor units at a higher fan speed than a lower one or have I got that the wrong way round?

richardc1983

Hi Swipe

It is very slightly more efficient to run them at high fan speed but this increases your noise level and people may begin to experience draughts around them.

The reason it is slightly more efficient is because your outdoor units become the heat collector (evaporato coil) and have a large surface area compared to your indoor units which have now become the outdoor units rejecting heat (condenser coil) these have smaller surface area than the outdoor units when used in heat mode so to move more air through the coil means more heat rejected.

However with your system being an inverter system the outdoor unit will only gather what heat is required anyway and the outdoor fan will slow down/speed up to gather what heat it needed for the indoor units.

This was really only applicable for fixed speed heat pump systems.

The indoor fan motors use about 5watts more electricity on each speed change so its not going to be noticeable whatever speed you use.

You will get faster warm up times with the high fan speed, so set it to auto fan speed and let the system do what it wants so it will warm up fast on high speed then revert to low for maintaining that temp.

Regards
Richard.

Swipe

Thanks, Richard, very interesting stuff

albyota

Hi Pace, my answers to your questions as follows: -
I ain’t a mathematician so go easy eh

Any idea how much oil and electricity you were using before the heat pump installation?

Unfortunately due to only having a small oil tank I could not buy in bulk, therefore I was buying in August and again in Jan or Feb, (premium rate) really frustrating so I was paying anywhere between 39p and 55p/L and I was getting through 1400 L / yr for heating and hot water 1400 x 41p Avg =574 +5%Vat = 603 + annual service 75 = 678.
Have just averaged up electric bills for 07 – 08 and into 09 and was paying avg. £62/month so £744 which just about cleared the annual usage. Accuracy + or - £30 due to increase in unit cost, change in habits, eldest son moving out, etc.


Does your system have some auxiliary heat switched in if the heat pump cannot maintain the set temperatures?

No, there is no other form of heating…no auxiliary, no electric boost, no gas, or oil..just the ASHP it coped very well this Feb at minus 8

If so, do you know how much that is being used and costs? See above


Does the heat pump make domestic hot water at 60 all the time, or do you have a daily/weekly "thermal disinfection" routine?

Due to my cylinder being the original installed, (standard coil length 0.9m2) it is not as efficient at transferring 58 degrees water supplied from the ASHP via the heat coil in the cylinder (for flow temps of 58 C the coil in the cylinder needs a greater surface area 3m2...longer coil).
Therefore it only gets the water temp to 52/53 degrees in 1 hour (hot enough for what we need). Once a week the immersion heater is set to come on for about 30 mins to raise the temp from 52 up to 65 for ‘thermal disinfection’.

I am constantly messing about trying different set ups / controls / timing etc. just replaced some analogue room stats for digital night set back stats and will see what results I get.
Hope this helps

richardc1983

Albyota what set points do you keep your rooms at and were you able to maintain those when we had days like new years eve where it didnt get above
-3C all day. My air to air heat pump system we were able to keep the house at 22C on these days but any warmer I think we would have struggled.

albyota

Richard, as I have Underfloor heating, lower flow temps are not a problem for it so can get the rooms to 25 if wanted but generally kitchen/ family room at 22 and lounge 23, kids bedrooms at 19 or 20 with night setback to 18, bathrooms 23 with UFH and towel rads, however, as there are 3 females in the house I am on a losing battle.....have you ever seen padlocks for roomstats?

richardc1983

HAHA U can get boxes that go around the stats to stop people messing with them!

albyota

and theres me just about to order a condenser security cage........

richardc1983

U could use one of those and keep the kids in it!

stevehead

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