Heat Pumps and thermal stores

[Inti]

Looking at increasing the portfolio of technologies that we can do and been looking at Air Source Heat Pumps.

On the face of it in the right situation these Air to water pumps seem to really have a lot going for them. When RHI kicks in even better.

But I am getting a lot of conflicting information the more i look into it.

Some say they are great for heating and hot water and others are saying that the temperatures required for hot water reduces the COP rating too much. Some suggest using a thermal strore with solar thermal and use the thermal store to supply heating and hot water. But this solution doesnt really address the temperature issue when there is no solar gain. I have even been told that a hot water coil on a thermal store will not work unless the temp exceeds 80 celsius and that really messes the COP ratings up.

Does anybody know anything about this technolgy and able to comment on ASHPs producing hot water?

 

[markfxy]

Most heat pumps will do 55° nowadays at a decent cop if you're using a thermal store it must be designed for heat pumps as they have a higher flow rate which will upset the stratification, use a store with a plate heat exchanger for hot water. Have a look at Panasonic Tcap they can maintain hot water temperatures even at low outdoor temps.

 

[jason121]

Heat pumps work from 45 to 55 degrees and some from 60 to 80 degrees. They work well with properties on LPG or Oil not so well with mains gas, has that is still relatively cheaper than electric.

Has I have said before design is critical for sizing heat pumps using heat loss calcs in buildings.

MCS state that they must do 100% of the space heating. Buffer tanks help maintain flow rates for systems also act has a heat battery, so the system can maintain temperatures when the heat pump goes onto defrost. To achieve the RHI, the emitter circuit must achieve 3 star using the emitter guide from MCS. Most installations pre 1995 will need Low temperature radiators installing to receive 3 stars. It’s not just a case of plug and play. You will need a good heating engineer if not one yourself and will need someone with G3 unvented and water regulations.

 

[Worcester]

@jason121 I belive that there is some kind of loophole that means that unvented thermal stores do not require you to have the unvented qualifications that are nescessary for DHW tanks... That is not to say that an unskilled person should attempt to install them.

We have come across some horrendous designs and installations that we can only described as not having been designed. Prior to Feb this year, heat pumps didn't have to provide 100% and could rely on the built in immersions - net effect horrendous bills. Getting the design right is crucial and it needs training and experience. There are lots of people that claim to be heating engineers out there, most are plumbers that rely on back of smoke packet calulations and a table from the manufacturer. GOOD heating engineers are hard to come by.

 

[BruceB]

I guess the loophole might be that a heat pump alone can never get a thermal store up to 100 degrees so there is therefore no need to put the standard G3 protection on them - provided there is no immersion in the thermal store or auxiliary heater in the heat pump. However, in my experience the thermal stores all come with the T&P safety valve in the UK and the heat pump manufacturers include them in their schematic diagrams of docking arrangements. Good luck convincing an MCS assessor there is a loophole!

 

[Worcester]

@BruceB It wasn't me that found it, it was the thermal store manufacturer, openly saying that you don't need the qualification to install them!!

 

[BruceB]

Probably then with the caveat I mentioned of no immersion heater.

The requirement to have the G3 certificate vanished in the latest (2010) edition of Part G. Now you just have to be competent, so if asked to provide evidence of competence the point may be moot.

 

[MCS Renewables]

You will need the unvented ticket but its a one day course and is a multi choice exam. The current qualification lasts five years.

Once you have done an approved heat pump course you can apply for an MCS registration and you will need to show them your test case project, so basically you need to go and sell a system and get your qualifications done before you get into the MCS.

However before you can fit the heat pump you will need to have done the manufacturers course so that it gets a warranty etc. You will have to do a course for each manufacturer of the kit you want to install so more expense and time off. Some will not let you on the course until you have Energy Efficiency qualification as well.

Once you are in the MCS every manufacturers heat pump salesmen is knocking on your door telling you they have the best kit , blah blah ....but you have to do their training course as well !

Also you need to do at least one project per year to maintain your registration which is the same for each technology. So unless you think you can sell at least five systems a year to cover your outlay I would be cautious about heat pumps.

The RHI is unlikely to apply to properties on mains gas (thats the way its heading) and the entire scheme is like the pot of gold at the end of the rainbow, sounds good but sort of hard to actually get hold of !
Furthermore the scheme gets booted down the calender, by government, with alarming regularity.

Air source heat pumps can cope with hot water easily, it is space heating that it is more of an issue.

Most heat pumps installations need an immersion for legionella control.

 

[CES Heating]

As previously said, You need your Unvented ticket. Its also not the plug and play option most people seem to think. Having said that if the property is properly insulated, the correctly sized heating emitters are fitted then a heat pump is certainly a good alternative to oil or LPG. I wouldn't even consider fitting it to a home which is on the gas grid as it doesn't stack up. With rising fuel costs who knows what will happen in the future.