@jamespa TBH man, im not near as knowledgeable to understand that. When you say 4-5kw, does that mean 2-2.5kwh usage per hour to heat the house to maintain temperature?

All i understand is KWH per hour usage and what is normal or not. Im in a new build very well insulated but house has got over 23 in living areas so lowering my curve to 36 -5 and 26@20deg. That will hopefully lower kwh usage. Haven't altered flow rates yet as some bedrooms still only 18 but presume since slab hasn't been heated since april it will take longer for them rooms to get up as not much solar gain.

1kW=1kWh per hour (kWh = kilowatts times hours, ie 1 kilowatt for 1 hour.  Kilowatt hours per hour is thus kilowatts times hours divided by hours, ie kilowatts - the hours cancel out).  So 4-5kW = 4-5 kWh per hour.

Reducing flow temperature will almost certainly reduce the consumption and may reduce the house temperature depending on what other controls you have (if you have TRVs/thermostats they might be determining the house temperature, rather than the flow temperature - best to set these a degree or two above your target temperature and let the flow temperature do the job).

The optimum (at least in the height of winter) is to operate the system pretty much 'open loop' with the system operating continuously at the lowest flow temperature at which it heats the house to a comfortable temperature and the TRVs/thermostats staying open/on.  Possibly a night time set back will help (thats the subject of discussion/analysis this thread) but it is s bit dependent on your specific circumstances. 

In general terms 'Low and slow' is the overriding general motto of operating a heat pump and that derives from the basic physics of how they work.  At this time of year solar gain means that it almost certainly does make sense to turn off at night and during the daytime, but once it gets cold and dark its generally better to heat 24x7 or thereabouts at the lowest flow temp possible.  So I would adjust again when it gets colder and when its very cold try to find the minimum flow temperature that just keeps the house warm enough if you leave it on 24*7.  That gives you at least 2 points on the 'weather compensation' (*) curve.

(*) Weather compensation is the term used to denote changing the flow temperature according to the outside temperature, so that the inside temperature remains constant at the lowest possible flow temperature, which occurs if the TRVs/thermostats don't have to switch off too much to maintain the desired room temp.  This should have been set up by your installer and he/she should have explained it to you.  Its a feature also available also on gas boilers but we tend not to use it in the UK (in some countries its been obligatory for decades to enable it).  Its is more important that it is enabled for heat pumps because of the physics of how they operate. 

Incidentally please rest assured that you don't need to know or understand the physics of how they work, just to be very aware that they get significantly more efficient as the flow temperature reduces.  This effect is large enough that that 'zoning' of houses is, in some circumstances, counterproductive because, although it reduces the heat demand it also reduces the active emitter area, pushing up the required flow temperature and thus reducing efficiency to an extent greater than the saving in demand.  Whether or not this applies is house specific, but the old assumption that zoning is a 'good' thing does not apply universally to houses with heat pumps.  

One vital question I should have asked.  Is '2kwh per hour' energy consumed (as measured eg by your electricity meter) or energy delivered (as measured eg by your heat pump - but note that your heat pump will also measure energy consumed so you need to read the display carefully). 

If its energy delivered then its a broadly reasonable figure.  You should in this case be consuming about 0.5kWh/h.

If its energy consumed then either

1. you are heating up the fabric in which case it should settle much lower in a day or two or

2. its very high, because it means you should be delivering 8kW, which is a lot, so either your system is very inefficient or your house is very lossy,

Please clarify

Posted by: @newhouse87

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So first day of heating season today. Temps in house were down to 19 in living areas and 16/17 in bedrooms. started my wc at 38-5 and 28-20 as per derek m suggestions. Currently flow rate at 34l/min and flow temp 28.4deg. Have it on since 7am.  Going to run until 9pm and then setback until 5:30am. House noticeably warmer already and living areas up 3 degrees to desired 22degrees, solar gain playing large enough part id imagine.

Would 2kwh per hour be normal for 242 sqm house.

Is your weather compensation set to 38C LWT at OAT of +5C or -5C?

I suspect that because your home is a new build, it may not have the internal thermal mass of older properties, and will probably have better levels of insulation. The fact that you mention a slab, would indicate that this may introduce additional thermal mass, which of course will require additional time to heat up and also cool down. Optimising the WC curve can therefore be a slow process, involving making say a 1C change at one end of the curve, and then monitoring the temperatures over a 24 hour period. It would also be useful to record the following readings at say hourly intervals when possible, the IAT, OAT, LWT, RWT and flow rate.

Solar gain, wind chill and rain effect, can cause changes in IAT for which the WC curve cannot accommodate, which can make adjustment of the curve more difficult. It may therefore be necessary not to over adjust the curve on particularly sunny or windy days, where the above recording of data may be of use.

Most heat pump controllers have the capability to set an offset to the value calculated by the WC curve, so on a sunny day when the IAT may start to increase, rather than adjusting the curve, once correctly optimised, the IAT can be lowered by an offset of -1C or -2C.

There is no actual 'normal' values as far as electricity consumption is concerned, since this will vary with the size of heat pump, the heat loss of the home, the OAT and the desired IAT, along with the above mentioned external effects which can occur. It is therefore necessary to record the operating parameters for your particular system over a period of time, then periodically check that your system is still operating correctly.

@jamespa its consuming 2kwh. Its first day since april heating the house. Hopefully il be able to adjust curve even lower then 36@-5. Started at 38 today and living areas 2 deg above desired.

1. @derek-m was set to 38 at-5. Reckon was bit warm as living areas went to 24, some due to solar gain but air felt warm. At 36-5 now and ill see how thst behsved tomorrow. Yes i have that offset on mainscreen. Any reason why pump is operating at13l/min flowrate now. Was 32-34 this morning when house colder.

Posted by: @newhouse87

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@derek-m was set to 38 at-5

Hopefully Derek will survive, and be able to tell us what the experience felt like.

An average 2kW consumption (if that is what it is) at this time of year is a lot.  You should be getting a COP of 4 ish or more, which means that the heat pump is apparently (or at least should be) delivering 8kW plus -  which, if its doing it 24*7, is a lot of energy.  Hopefully you are heating up the slab you mention and it will reduce significantly, or alternatively your 2kW is not a 24*7 figure.

Where are you, whats the flow temperature currently (as opposed to the flow temp at -5) and is the heating on 24*7 or only periodically?  Is it really 2kWh/h 24*7 (ie 48kWh/day) or is it a lot less?

As @derek-m says you need to monitor and record over some time to get a proper read out of how your system is performing, and as he also says optimising the WC curve is a slow process.  Nevertheless, if you really are consuming ~48kWh/day (and thus hopefully delivering 192kWh/day) at this time of year, that's quite a lot of energy going somewhere. 

Posted by: @derek-m

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I have now completed some further improvements to the modelling tool.

It is now possible to adjust the desired IAT setpoint and also the OAT value to one decimal place. This therefore provides the capability to ramp up and down the setpoint and more closely match variations in OAT.

Have fun in the 'Playroom'.

I downloaded your modelling tool but there are lots of '#value' in the playroom.  Is there something I need to dial in to start it working?

@jamespa i turned heating on at 7am and setting it to go off at 9. Flow temperature 29 alot of the day, think i can get that lower over coming days.Just checked itvhas used 23kwh over 12hours. Pump has now gone off as i think delta t is at 3 and not specified 5. House warm now especially living areas so can adjust lower. Quite cold approx 10deg today. 6degrees now. Somedays last year were consumingbup to 70kwh. So today seems like big improvement running constanntly and was heating floor slab first time since april.11kw daikin low altherma 2 pump i have.

@newhouse87 OK sounds more reasonable then, you are most likely heating the slab.  As @derek-m says there is no 'right' figure, it depends on the house and outdoor temperature as well as other factors.  Monitor over several days and see what happens!  You need to aim for a position where you don't have to adjust the flow temperature and the heating is on most, preferably all, of the time (unless you deliberately switch it off of course).  But again as @derek-m says adjusting the WC curve is a slow process to be carried out over some months to experience a range of conditions.  If only we could tell the weather to stay at 10C for a few days, and then stay at -5 for a few days!

@jamespa ah hoping to heat 530am to 9pm. Noise of pump keeps me awake. Hoping that house being well insulated will have reasonable heat loss overnight. Thanks for all the info. This forum is invaluable to people like me as installer told me zero and i mean zero.