Not Happy with Air Source Heating

[Norcon]

Why are air-water heat pumps so expensive?
They add nothing more than a £100 quid plate heat exchanger and price it in as another £3 grand or so.
What a rip off.

A panasonic air/water Aquarea T-Cap 12kW Monoblock is £5 grand inc vat and delivers 12kw.

An LG Multi split air/air with eight indoor units gives a combined heating capacity of 20kw is £2769 inc vat.

So you have the heat emitters included and another 8kw of output for nearly two and a half grand less.

Air/water is little more than a gimmick foisted on the domestic market.
Manufacturers have seen the opportunity and are milking it for all its worth. Foolish government subsidies are not helping either.

 

[kevobain]

Re the hot water

1) the temperature should be raised to 60ºC once a week to sterilise the cylinder.

2) Heat pumps aren't great for heating hot water as the required rise in temperature is greater than they can normally deliver particularly in cold weather. Grant do sell a hot water boost kit. http://www.grantuk.com/products/cylinders/grant-heat-pump-cylinders/ Is this part of your installation.

Domestic Hot Water Boost kit
Whilst it is possible to raise the DHW to 60ºC with an Aerona Air Source Heat Pump, it can be more efficient to set the hot water temperature between 45ºC and 50ºC and utilise Grant’s Domestic Hot Water Booster Kit to take the cylinder up to the desired higher temperature. This unit comprises an enclosure with 20A rated contactor, an override switch and relay, which works with the immersion element fitted in all Grant cylinders.

Re the heating

1) A lot of the problems with heat pumps stem from undersizing them. However, in your case I think the problems may relate to an over sized heat pump as you've a well insulated house. If the heat pump is oversized it cycles as reaches temperature quickly. Start up consumes a lot of electricity.

2) The installation should have a buffer vessel to minimise start ups.

3) The heat pump may be going into defrost mode a lot if the temperature has been cold. In such circumstances electricity consumption is high.

4) The heat pump is faulty.

5) The Grant units are Chinese made and have not been specified for UK climates and you can find numerous threads about problems with them such this one. http://www.ukplumbersforums.co.uk/renewable-energy/19157-grant-air-source-heat-pumps.html

6) Air source heat pumps aren't always as cheap as claimed. The EST did a study that found most installations they study has a COP of 2. You need a COP >2.7 to beat an oil boiler and if you are on mains gas they are a non-starter. This thread is a good summary of the issues. http://forums.moneysavingexpert.com/showthread.php?t=2968958

Personally I would rip it out and replace with an oil boiler. This would be easy to do you would just need to blend in to the underfoor circuit. I also think you should pursue the installer for recompense as the system clearly has not been set up/specified correctly

Thank you very much for the response. I've tried a few different things with my heating since I last posted in the thread. None of them have been overly successful.

Firstly though, I think I actually have the HW boost kit fitted so I don't think I should have to heat the cylinder to 60° every week?

The one thing I tried after being advised was to put my pump on 24 hours a day as it should start and stop less etc. That didn't work. My daily costs went up approximately £4 a day!! However, I must admit that the system did manage to get the house nice and warm. I was worried before that it wasn't working correctly. I've now reduced the on time to come on for the all of the off peak rates. The house is warmer and I'm back down to about £7 a day. I've also stopped one of the heating periods for the hot water so am down to two per day. I tried going down to one but we didn't have enough hot water for two showers and my son's bath in the evening. Two seems to work just fine now.

I might actually look in to getting the system replaced with an oil boiler. Does anyone have any idea how much it might cost to do this job? I've got to the stage that I could probably live with the air source but I'm still not overly fond of it. It's really not living up to my expectations and it's the only thing I don't absolutely love about my house. I could try and get recompense from the installers but I don't fancy my chances. Not sure what the market would be like for 2nd hand ASHPs or if Grant may even take it back. Who knows, it's definitely worth looking in to though.

Kev

 

[dcawkwell]

It's the immersion heater in your system kicking in that is causing your problems.
See the manual as per my previous post.

 

[SilentDancer]

Firstly though, I think I actually have the HW boost kit fitted so I don't think I should have to heat the cylinder to 60° every week?

Correct if the temperature is being raised to 60°C. An option is turn the temp down on the cylinder and sterilise once a week or so. The risk of legionnaires is exists but is unlikely.

The one thing I tried after being advised was to put my pump on 24 hours a day as it should start and stop less etc. That didn't work. My daily costs went up approximately £4 a day!! However, I must admit that the system did manage to get the house nice and warm. I was worried before that it wasn't working correctly. I've now reduced the on time to come on for the all of the off peak rates. The house is warmer and I'm back down to about £7 a day.

The fact that you ran the heat pump for 24hrs and the heating bills went up suggest that the pump may be oversized. The house is reaching the set temperature and is cycling. Start up use a lot of electricity.

I've also stopped one of the heating periods for the hot water so am down to two per day. I tried going down to one but we didn't have enough hot water for two showers and my son's bath in the evening. Two seems to work just fine now.

Another problem with your system seems to be that the cylinder is too small. Looks like it is 150L. Should be 200L + for a family home with mains showers.

I might actually look in to getting the system replaced with an oil boiler. Does anyone have any idea how much it might cost to do this job? I've got to the stage that I could probably live with the air source but I'm still not overly fond of it. It's really not living up to my expectations and it's the only thing I don't absolutely love about my house. I could try and get recompense from the installers but I don't fancy my chances. Not sure what the market would be like for 2nd hand ASHPs or if Grant may even take it back. Who knows, it's definitely worth looking in to though.

I guess about £2K to £3K to replace with an oil boiler depending on the work that is required. One thing that needs doing is the underfloor circuits will need blending. Worth contacting Neil Sawers, Grant's Technical Manager to try and fix it or see if they'll do a deal on an oil boiler.