Advice needed on ASHP

[jason121]

Can someone verify that when retro fitting the heat pump system for Radiators, to achieve the maximum RHI, the designer must design the system at 45 degrees and replace all Radiators as per the emitter design guide??????

OR

If designer leaves existing radiators, design the system between 55 and 60 and receive a lower rate RHI??????????

 

[The Solar King]

RHI not yet fixed. Consultation I think closes on 9th December. Have a look as the MCS standard MIS3005, guidance MGD002, and heat emitter guide MCS022. All downloadable from here:
Microgeneration Certification Scheme - Installer Standards

 

[jason121]

I have all the documents just wanted to hear from another installers view on this subject, how can you sell heat pumps without knowing if its ok to keep existing rads or need to change them all to qualify for RHI.

 

[The Solar King]

I do not sell heat pumps or fit them. What is clear is that to get the maximum from a heat pump you need to deal with the thermal performance of the building fabric and use heat emitters that are suitable and matched to the performance of the heat pump.

As the purpose of the RHI is to pay for renewable heat, it is possible that the tariff will be based on a 3 star rating for emitters attached to a GSHP and a 5 star rating for a ASHP. This would mean an estimated CoP greater than 3.1 The carbon emissions of a heat pump would then be lower than a gas boiler. As previously stated RHI is still out to consultation and no decisions on the proposals have yet been taken. It is just about certain that RHI payments will be based on deemed performance. This being the case, it will assume a certain level of performance. If an installation does not meet this performance level, payments will not stack up against running costs.

 

[ktech]

We have completed the Samsung training and I have installed a HP in my own property. You really need to do a full property (room by room) heat loss calculation. The software we use works on a 18-21 degree room temperature (depending on room type / usage) at 50 degree output of the pump (the pump will run at 55 degrees in reality but this builds in a bit of room into the equation). The heat loss calculation then shows which rooms need upgraded radiators. Personally I wouldn't fit a system for someone if they didn't want to upgrade the suggested rads. From experience not all rads need upgrading, may be 50% in the average property just depends how oversized they originally are. I don't even look at the RHI when specifying a system it's more to do with making sure the system will perform. From my understanding the RHI (when it comes out) will apply to MCS accredited systems and as part of the process you will have done a heat loss calculation to make sure it provides 100% of the heating and DHW upgrading rads and tanks when necessary.

 

[FB.]

While on the subject, I've seen mention of ASHP's possibly being eligible for 6.9p to 11.5p per kWh, but how do they intend to calculate that?

Reason I ask is that I'd be interested to try an ASHP if it's a viable option compared to my existing heating system, which is a 22-year-old Potterton gas central heating that probably doesn't have much life left in it.
The system wasn't as well-designed as it should have been (fitted when house was built), with the lounge being considerably under-spec'd (a single 6000BTU rad but needs more like two 5000BTU rad's according to a plumber friend of mine) and we often have to use a small 500W electrical heater running all evening to give the lounge an extra couple of degrees boost.

So making changes to the rads, along with TRV's, could actually be a blessing, to deal with the under-spec lounge.

For curiosity, here are the temps of the rooms, with theromostat in the dining room set to 20'C:

Diner: 21'C
Lounge: 19'C *
Hallway: 19'C
Landing: 18'C
Bedrooms: 18'C
Bathrooms: 18'C **
Unused rooms: 15'C (rad turned off and door closed if not in use)

* Addition of a 500W conservatory electrical heater brings the lounge up to 21.5'C so that the wife doesn't have to hide under a blanket.
** 750W infrared electrical heater ensures bathroom has a temperature boost available if needed - such as when the water isn't pumping round the rad's due to downstairs being 21'C.

Some would day "turn down the dining room radiator" but the heating system is slow to heat up (1'C every half hour) and we need all the downstairs rads on max in order to get the house warm quickly enough (lounge and diner are connected by double doors so the diner helps to heat the lounge). The rads all get very hot and are bled regularly, but there just aren't enough of them and/or inadequate sizes, to get the heat into the rooms.

 

[ktech]

As I understand it the 6.9p to 11.5p per kWh is the band that is out for consultation. The RHI is proposed to be paid on the renewable energy (i.e. if a COP of 3 then 2 units are paid for as it took 1kW of electric to generate 3 kW of heat). The tariff will be for 7 years and this is reflected in how generious the tariff is. I guess one way to describe it is that you purchase one unit of electricity at 14p and because you get 3 kw (as an example) of heat out you get 2 x 6.9 to 11.5 in RHI. I expect the annual RHI payment will be capped depending on some part of the heat loss / MCS calculations - otherwise you would probably leave all the windows open !

 

[zeljuga]

You need to change them anyway as existing radiators are designed for gas, or oil boiler . Assuming 80`c system flow ,compare to ASHP where flow is 35 to 45`c in optimal SAP performance. Anything above will substantially reduce efficiency of ASHP to the beyond economical point.
Small chance to keep existing reds if you improve overall insulation to the point of exs. rads . matching heat loss calculated with CH flow of 35`c.
ASHP ideal for underfloor heating . Optional convector radiators which give you about 30% increase kw output for same size radiator.
Hence RHI is only drop in the water in complete equation ,like iceberg .

 

[FB.]

So if my house currently uses 12000kWh equivalent of gas per year (about £640 at my current prices), then an ASHP with COP of 3 would require 4000kWh of electricity (about £500 at current prices, ignoring standing charge). During daylight - especially in autumn and spring, but also weekend days in winter - my 3.75kWp solar PV array would make a worthwhile contribution towards the power requirements, albeit erratically depending on weather.

So an ASHP would achieve:
1. A replacement of the 22-year-old gas boiler which probably doesn't have much life left.
2. A modest reduction in my bill.
3. An opportunity to get the right rad spec for the lounge.
4. An incentive payment in the form of a FiT.

So if I have an ASHP (COP3) which consumes 4000kWh of electricty per year, to generate 12000kWh of heat equivalent, for a net difference of 8000kWh of heat "from thin air", I'd expect a FiT of around 8000 x 6.9p to 8000 x 11.5p; £552 to £920 per year. For seven years, totalling: £4k to £6.5k in payments.

I'm liking the sound of this.......where do I sign?

 

[ktech]

I would say you are sort of on the right track but its a bit simple using just a cop of 3. I can see it now that customers will just look at the cop of a unit but in reality its more than that. It's about a well designed and sized system. The cop rating will be at a specific outdoor temperature etc.., a bit like PV panel stats at x metres2 of y radiance - it's a great headline figure that customers use to compare and the suited and booted sales man uses but no full picture. So a full heat loss calculation takes a lot more into account than the cop of the unit e.g. floor type, window type roof type etc.. The solar pv is nice to have but your pv will generate the most beneficial electric when the air sourced is not working very hard and the pv will be doing the least when the HP is battling against low temperatures, however the FiT for the year can all the same be put against your electricity cost on an annual basis. Even if you have a recent'ish tank expect to replace it with a HP tank with large surface area coil. A well designed system will run 24/7 working with outside temperature compensation. As an example you don't turn it off when you go out as it could take a long time to bring the building back up to temperature (without ending up with a massive bill as the HP tries to recover). You may even think the radiators are not work as the system will just maintain room temperature working as hard as it needs to based on outside temperature and the internal stat. I've been very impressed with my system. Also forget drying your washing on the radiators - not that is has ever been a great idea to lag your radiators with clothes anyway!

 

[FB.]

customers will just look at the cop of a unit but in reality its more than that. It's about a well designed and sized system. The cop rating will be at a specific outdoor temperature

Yes, with an under-spec'd lounge I can appreciate not cutting corners is necessary to get the best out of the system.
I've also seen data suggesting COP=3 is for around 10'C outdoors, dropping to COP=2 around freezing, and COP=1 around -10'C. Or something like that.

I appreciate that the solar will only make a partial contribution, but every little helps. My 3.75kWp array tends to output a few hundred Watts for a several hour period on dull days in spring or autumn, and up to 3.6kW at peak power for a couple of hours a day on sunny days from spring through to autumn.
Peaking only around half power now for a couple of hours on bright days, and on days like today when daylight never arrived its only managing maybe 100W output for several hours - most of which the fridge is probably using!

In many ways, though, I would also be keen to try because I am somewhat eco-friendly (and a grow-your-own type of person) without being a fanatical "green". I am also formerly a scientist by trade, so I have a natural interest in experimenting with new ideas and technologies.

 

[TedM]

The RHI you might get will be based on a deemed amount of heat your house requires calculated with RdSAP-style software. The kWh you actually use will be irrelevant. And it is still possible that DECC will decide that RHI is not going to be available for those on the gas grid.

 

[The Solar King]

Last comment I heard from Patrick Allcorn (heid yin of domestic RHI) of DECC was the intention was to include on-grid areas but that because gas is available, the RHI would not be all that an attractive proposition.

 

[BruceB]

from a horse's mouth a week or so ago

 

[jason121]

As i understand it if using existing rads = a 1 star rating on emitter guide = low RHI payments
Under floor heating or Low temp Rads running between 35-45 degrees = 3-4 star rating high RHI payments.