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Author Topic: Intermittent Heat  (Read 1966 times)
applesandgravy
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« on: November 22, 2013, 11:10:13 AM »

When calculating heat load figures for a property should an allowance be made for "intermittent heat load".

If so how much? and if so is it good practice to do it, or is it convention to do it, or is it MCS regulations to do it? or British Standard?

or is it as an MCS installer has just told me. "not needed as a heat pump can not be used intermittently as it is on all the time"

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dhaslam
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« Reply #1 on: November 22, 2013, 12:59:44 PM »

It is preferable to only use  off peak electricity  and  also to run the heat pump constantly when it is on.      The cost of heat pumps is so high that installers find it easier to sell smaller systems that run around the clock  and even use  immersion backup in cold weather.   Everything is quite costly  in scaling up the system to use off peak electricity.  A buffer tank is probably  needed, the ground loop may need to be a bit bigger and the unit has to be bigger, possibly exceeding normal  electrical   connections.  It is really a question of balancing  capital cost against long term  savings.       
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
applesandgravy
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« Reply #2 on: November 22, 2013, 01:23:05 PM »

i forgot to mention that i am trying to size a ASHP.
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dhaslam
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« Reply #3 on: November 22, 2013, 02:28:13 PM »

There isn't quite the same set  of  circumstances for ASHPs.   The air is warmer during the day so there isn't  as much  advantage to using off peak electricity, at least  night time electricity.   However in   typical British Isles winters there are  night time temperatures of  10C or more and it is good to be able to avail of the  lower electricity rates and in frosty weather you can still just use  the heat pump when the sun comes out.    An ASHP wastes a lot of electricity if it stops and starts, it can be  running the fan and circulation pump for several minutes before the compressor starts and then takes a little time to warm up as well, even a small buffer tank can  be enough to keep it running for a set time each day  and  also can provide extra heat at peak times.           
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
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