ASHP's and the maze of info

clockworks_2

thanks for your post Cardew and explaining it. My flat only has electricity so i guess it's a lot better than storage heating or plain electric heating.

I was advised it's better to leave the system running 24/7 rather than on and then off . As it puts more pressure on the system heating from cold than leaving it ticking over.

What would you say?

Cardew

clockworks wrote: »

thanks for your post Cardew and explaining it. My flat only has electricity so i guess it's a lot better than storage heating or plain electric heating.

I was advised it's better to leave the system running 24/7 rather than on and then off . As it puts more pressure on the system heating from cold than leaving it ticking over.

What would you say?

There are posters here far more qualified than I on ASHPs.

However it doesn't matter how long you have the system switched off or turned down as it won't cause it harm.(i.e. put it under pressure)

The problem with ASHPs is the have a relatively small heat output,(compared to conventional CH) especially in winter when the COP is lower.

Thus it takes much longer to bring a cold flat up to temperature than a conventional CH system. Richard's oversized units take two and a half hours to raise his flat by 8C which illustrates my point.

If you are out at work all day, it will not hurt to switch your ASHP off or turn it down, as long as you set it to bring it up to the temperature you require when you are back in the flat. e.g. If, say, you went out at 8am and returned at 6pm, you could have the heating to go off at 7:30am and back on at 3:30pm. You would need trial and error to get the timings to suit your flat.

richardc1983

Cardew wrote: »

Also keeping doors open to bathrooms, bedrooms etc.

You dont have to leave doors open if you have a unit in every room and one in your hallway, the heat from the hall would then get into the bathroom.

We leave our bathroom door open anyway when not in use to stop damp etc.

richardc1983

Cardew wrote: »

Exactly!!

How long with conventional Gas CH? --- 30 mins???

You must have a very large system because this house takes nearlly 4 hours for the room temps to raise 22C from the same 15C.

There are massive radiators and the boiler is set on 84C also its because its a victorian house.

my parents house also takes about 2 hours to warm up to reasonable temp as does most of peoples I know the only house that doesnt is my friend and her house was built in the last 10yrs and hers warms through within an hour.

The way air to air systems deliver the heat is quicker than radiators as they move more air.

Its 3C outside here I switched the system on at 13.30 internal temp 15C and were now at 20C so only another 2C to go and were fine again.

richardc1983

Cardew wrote: »

There are posters here far more qualified than I on ASHPs.

Thus it takes much longer to bring a cold flat up to temperature than a conventional CH system. Richard's oversized units take two and a half hours to raise his flat by 8C which illustrates my point.
.

THe units are oversized but even in these weather I run the fans in low fan speed, if I bump them upto high we reach set point in nearlly an hour however we have added noise then.

If the units were undersized you would have to run them in high fan speed all the time and would never achieve set point.

I prefer to run them in low as the place still warms up faster with the air con on than the central heating.

As posted in another thread the system coped fine at -5 outside and we didnt have any loss of duty, just longer running times which I prefer as it means we have warm air constantly circulating the room rather than when it reaches thermostat off where we then have a 1C drop in room temp before it comes back on which can be felt in an old house like this with very high ceilings and no insulation.

thechippy

To (try to) answer some questions…

1. I must disagree that a gch system will warm a house faster than an air to air system.:p:D
My house, as Cardews will go from say 15-22 in around 45 minutes with the rads at 80c.

However, a “correctly” sized ashp can do it in minutes.

A couple of examples……

Today, I installed a Fujitsu air to air inverter in a large staff canteen, as the ancient one that was there had failed. The room was nippy to say the least.
Upon starting the Fujitsu, the room was toasty in about 10 minutes. The staff started to moan it was too hot.

Last year, during the very cold weather / snow, I installed a Mitsubishi inverter in a conservatory. Now believe me, this room was uncomfortably cold, even wearing 2 sweatshirts and a fleece! Again, I would say that the room was t-shirt temperature in less than 15 minutes.

As stated before, the problem is undersized systems.
Richards problem may simply be the poor insulation and the fact he has the high Victorian ceilings.

2. It won’t do the systems any harm leaving them off, so when switching on they ramp up to full tilt, they will cope with that fine.

3. Defrosts. This is not the issue it was years ago.
It used to be performed pretty much on a timer only, normally every 90 minutes and terminated by generally erratic electro mechanical thermostats.
It is now controlled by clever electronics and sensors, so is only initiated when necessary and only as long as required. The Fujitsu today, took 2 hours before it went in defrost cycle and it was only for about 5 minutes. The indoor fan stopped and there was no real sense of any cold air falling from the ahu. It then went into pre-heat mode for a minute and the fan re-started. Leaving the fan on auto is generally best, as the computer will run the fan at the appropriate speed according to the info given by the sensors. Remember, that the better (more expensive) systems will have a far superior control strategy to the cheaper tat.

4. In domestic situations, imho, air to air is best, but only if you have an ahu in each room. Ducted systems give no individual control (unless you use thermostatically controlled electronic dampers - expensive!). I know Steve heats a general area and leaves doors open etc, and if he is happy with that, then that’s fine, but many people would not be.

5. There are other means of on demand hot water, than electric.

Such as….http://www.caravanaccessoryshop.co.uk/index.php?_a=viewProd&productId=1240

These systems are common in Spain for example, in rural areas. The gas bottles can be hidden away and last a surprising amount of time.

richardc1983

thechippy it is certainly to do with the insulation in this flat and the fact that below my lounge and other rooms in the flat is just a very cold cellar where the waste pipes from the kitchen froze up the other night so it must be freezing in there.

The heat will just be absorbed by the walls straight away.

My bedroom however which is the largest room in the flat can heat upto 22C within about 15minutes there is a flat above and below this room so I guess insulated by the other flats and only one outside wall in here so this shows that the system can heat up far quicker than the gas central heating.

Air blows out of the units at start up at about 45-50C this is probably about the same temperature of air coming off the top of the radiators when they are set at 80C however radiators do not force that air round the room and its only slow currents.

thechippy

richardc1983 wrote: »

thechippy it is certainly to do with the insulation in this flat and the fact that below my lounge and other rooms in the flat is just a very cold cellar where the waste pipes from the kitchen froze up the other night so it must be freezing in there.

The heat will just be absorbed by the walls straight away.

My bedroom however which is the largest room in the flat can heat upto 22C within about 15minutes there is a flat above and below this room so I guess insulated by the other flats and only one outside wall in here so this shows that the system can heat up far quicker than the gas central heating.

Air blows out of the units at start up at about 45-50C this is probably about the same temperature of air coming off the top of the radiators when they are set at 80C however radiators do not force that air round the room and its only slow currents.

Agreed.......;)

richardc1983

And again it depends on how much heat your house loses such as mine, my lounge loses heat very quicker whereas the bedroom retains it.

thechippy

richardc1983 wrote: »

And again it depends on how much heat your house loses such as mine, my lounge loses heat very quicker whereas the bedroom retains it.

....Which is why I keep reiterating to people that the heat load calcs need to be done correctly. Too often, they are half guessed or just worked out on the cubic metres of the room/s - doesn't work!...;)

Anyway Rich, you ok?