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Author Topic: Daikin LT ASHP: Optimising Settings  (Read 3023 times)
wytco0
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« on: October 30, 2012, 10:47:51 PM »

I am trying to work out the best options for my LT system which consists of the following units:

•Heat pump outdoor unit is a Daikin ERHQ016BAV3
•Heat pump indoor unit is a Daikin EKHBH016BB6V3
•Hot water tank is a Daikin EKHW5U300B3V3

DHW
We have a 5 bed house which is highly insulated and normally only has 2 people in it. We have showers between about 0600-0900 most days and then use almost no hot water for the rest of the day. We also have 2 solar thermal panels which may heat water during the day. We have been living in the house for about 7 months now and with DHW on all the time it heats water every hour or 2 for a few minutes, even when none has been used, as soon as there is demand it heats as well (as expected).

I am now going to put a timer on for DHW but I can't decide the best times to set.

My initial thought was to set the DHW timer to run from about 0400-0800 which should mean hot water for when we shower and a good change that it will be reheated after the shower. However this will also probably be the coldest time of the day outside which will mean the ASHP will be working hard and be less efficient. So next thought was run it for about 4 hours from approx 1600-2000 and then again for 1 hour from 0500-0600. This would probably be more efficient in terms of the pump but I am not sure how much heat will be lost dirung the night from the tank and if 1 hour will be enough for reheat.

Obviously I also want to gain from any solar heat I can pickup during the day.

Heating
Heating is set by individual room thermostats, currently bedrooms are set to 19C and living rooms to 21C this seems to be working OK, there are no timers and heating can come on at any time.

We are averaging about 20kwh per day overall for the whole house and I am interested in anything I can do to optimize the heat pump settings for the way we live so any thoughts on changes we could make would be appreciated.
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Countrypaul
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« Reply #1 on: October 30, 2012, 11:09:26 PM »

WHat electricity suply do you have, for example do you have E7? This could make a large difference as to when is the optimum time to run a HP in terms of electric costs.

From my understanding having a HP come on for just a few minutes every hour or so is not the best way to use a HP. What controls do you have for determining when the HP comes on, could you have a larger temeprature diffference between off an on thereby allowing the HP to come on for a longer period less often.

How large is the tank and is it just DHW, or is it a Thermal store?

In more general terms do you need all the bedrooms at 19C all the time? Could you use time setting on the various rooms so that for example, the living rooms are allowed to be cooler during the night (and possibly the mornings?).

Paul
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brackwell
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« Reply #2 on: October 31, 2012, 09:38:21 AM »

Perhaps you should start by reading this http://www.heatpumps.co.uk/DHW.htm  There is even a live output!

The basic principle is to keep all heat pump output temps to as low as you can get away with, even if this means they are on for a large part of the day.  This is the opposite to intuition and the reverse of gas boiler mentality.

As a background note that the big problem with DHW storage tanks and pipes is heat losses which are considerable (read summer DHW here  http://www.energysavingtrust.org.uk/Publications2/Housing-professionals/Heating-systems/In-situ-monitoring-of-efficiencies-of-condensing-boilers-and-use-of-secondary-heating-trial-final-report ).  Therefore if you want to chase min energy then you need to turn the tank temp down as low as poss say to about 42C  and this will improve the COP of the ASHP.

As you know a 1C reduction in room temp reduces energy consumption by 10% and i think most people here would say your temps are too high bearing in mind a modern non draughty house.  This again would improve the COP of the ASHP.     Close down the unused bedrooms.

If you are serious you could probably 1/2 your present consumption.

My preferred approach to ASHP + DHW is to improve the COP by heating the tank to around 25C when the losses are virtually nil and then use a inline electric heater for the showers. This will save money only if you have sensible showers say 8/10 l/min for say a total of 5/6 min.

Ken
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wytco0
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« Reply #3 on: November 07, 2012, 11:59:22 PM »

Perhaps you should start by reading this http://www.heatpumps.co.uk/DHW.htm  There is even a live output!

Thanks interesting read

The basic principle is to keep all heat pump output temps to as low as you can get away with, even if this means they are on for a large part of the day.  This is the opposite to intuition and the reverse of gas boiler mentality.

As a background note that the big problem with DHW storage tanks and pipes is heat losses which are considerable (read summer DHW here  http://www.energysavingtrust.org.uk/Publications2/Housing-professionals/Heating-systems/In-situ-monitoring-of-efficiencies-of-condensing-boilers-and-use-of-secondary-heating-trial-final-report ).  Therefore if you want to chase min energy then you need to turn the tank temp down as low as poss say to about 42C  and this will improve the COP of the ASHP.

Interesting it does seem counter intuitive but I am happy to give it a go. I think most ASHPs are set to higher that 42C, does setting the DHW to 42C also affect the underfloor heating? I am not sure what temperature we shower at but its probably somewhere near 40C, the so heating the water to a lower temperature would mean that we use more hot water from the tank and less cold water.

As you know a 1C reduction in room temp reduces energy consumption by 10% and i think most people here would say your temps are too high bearing in mind a modern non draughty house.  This again would improve the COP of the ASHP.     Close down the unused bedrooms.

The problem I have is that the other people in the house both think its cold, I know that most of the house is 21C most of the time with the current setting however in the large lounge where we have very big triple glazed windows there is a significant draft in the room which I think is cause not by any leaks but by a temperature gradient across the room with the windows being approx 3-4C colder that the position of the thermostat, the windows even though they are efficient for windows are still pretty cold. I have shut down the unused bedrooms to about 13C and a couple of them to 8C!!


If you are serious you could probably 1/2 your present consumption.

My preferred approach to ASHP + DHW is to improve the COP by heating the tank to around 25C when the losses are virtually nil and then use a inline electric heater for the showers. This will save money only if you have sensible showers say 8/10 l/min for say a total of 5/6 min.
Ken

Very interesting how do you do the calculation to see if this is worth doing? does heating the tank to only 25C low affect the temperature of the Underfloor heating?
 
« Last Edit: November 08, 2012, 12:01:02 AM by wytco0 » Logged
rt29781
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« Reply #4 on: November 08, 2012, 07:33:42 AM »

Remember that an air source heat pump is most efficient when the outside temperature is at its highest.  Ideally you should heat your water after lunch when daytime temperature is at a maximum.
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Nowt currently, Aberdeen.....well actually very well insulated extension with passive solar that seems to heat the house....
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