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.

 

[FB.]

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.

With the horror stories surrounding condensing gas boilers - breakdowns, maintenance and expenses - I'd rather take my chances with a heat pump!

I would have thought that houses like mine, in need of a new/improved heating system (or at least a boiler) ought to be among the first to have retro-fits of new technology for trials. Solar and ASHP on a middle-aged property would be an inspirational push into renewables.

But if they want me to reduce my carbon emissions, it would be crazy to encourage me to keep burning the gas. But if gas ends up being the cheaper option then I'll carry on chugging out the CO2 with the old inefficient boiler (75% efficient when new, probably 65% now).

 

[FB.]

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.

It would be a shame to encourage me to keep using gas (and emitting CO2) when there's the prospect of adding a lower-emission technology, particularly so as I would be eager to have a heating system reconstruction during summer 2013.

But as per my previous post: my tired old boiler can keep pouring out the CO2 if they want to make my life difficult.

For what it's worth, I think I'm a low-user.
4-bed detatched, used 10810kWh gas (about £550*) and 3139kWh electric (about £450) in 2011, according to my bills.

*Average gas bill reported to be £650 during 2011.

 

[jason121]

Mono bloc are good, no boiler inside, the heat exchange built in the main unit, you will need buffer tank and proberly a new hot water tank. Panaonsonic TCAP are good maintain full KW rating down to -15

Change radiators to low temp ones run them at 45 degrees cheap heating. Hopefully RHI will cover 90% of install cost over 7 years

 

[sambotc]

Star rating relates to the size of the radiator compared to the heat requirement. The bigger the radiator the lower the flow temp can be, lower the flow temp and heat pump doesn't have to work as hard meaning less electric used and a more economical system.

Solely reducing the flow temp will mean you have cold people! Also remember that lower the flow temp and you increase the warm up times, opening a door for 10 seconds in winter could take an hour to recover from.

 

[jason121]

the RHI want a SPF of 3 before they will pay out the higher rate

 

[sambotc]

With the horror stories surrounding condensing gas boilers - breakdowns, maintenance and expenses - I'd rather take my chances with a heat pump!

I would have thought that houses like mine, in need of a new/improved heating system (or at least a boiler) ought to be among the first to have retro-fits of new technology for trials. Solar and ASHP on a middle-aged property would be an inspirational push into renewables.

But if they want me to reduce my carbon emissions, it would be crazy to encourage me to keep burning the gas. But if gas ends up being the cheaper option then I'll carry on chugging out the CO2 with the old inefficient boiler (75% efficient when new, probably 65% now).

I decent condensing boiler installed professionally by someone who knows what they are doing (and a lot don't believe me) should be fairly reliable. A lot of the horros stories come from poor installations and early condensing boilers.

 

[sambotc]

forget the RHI. You are installing a system that needs to be able to cope with the properties heat load without using a shed load of electric. The star rating reflects the CoP which will indicate how efficient the system will be. Chucking in a system on the basis of RHI payments is not how it is intended and is heading towards failure. These aren't 'luxury' items like a P.V array. Mess it up and people are going to get cold or run up huge electricity bills.

This is the problem with renewables and the tariff they offer. Everyone has there eye balls stuck on the financial gain rather than their intended purpose.

As a heating engineer I can see this heading down the same road as the FiT's, and actually see the reasons for the delays.

 

[FB.]

How reliable are ASHP's and how easy are they to get repaired - especially relative to the ease and speed of getting someome to repair a gas boiler.

What's the realistic lifespan of an ASHP and what kind of warranty and ongoing maintenance and repair costs are likely?
With a motor running many hours per day, for several or more months per year, that's a lot of wear on a major moving part.

 

[Earthstore]

Your fridge and freezer run 24 hours per day, 365 days per year, how long do they last?
It is the same technology...

 

[FB.]

I decent condensing boiler installed professionally by someone who knows what they are doing (and a lot don't believe me) should be fairly reliable. A lot of the horros stories come from poor installations and early condensing boilers.

In my case, though, even the best boiler would struggle to do the job as the rads are under-spec in the major living area.
Go out for the day and leave the heating off, to find it dropped to around 17'C while out and takes two hours to get back up to 21'C.
Rads are hot (too hot to touch), but just not big enough to give off enough heat.
Complete system re-design would be a good idea - and I'd love to take the opportunity to try a well-designed ASHP system, if only to serve as a warning to others!

 

[jason121]

forget the RHI. You are installing a system that needs to be able to cope with the properties heat load without using a shed load of electric. The star rating reflects the CoP which will indicate how efficient the system will be. Chucking in a system on the basis of RHI payments is not how it is intended and is heading towards failure. These aren't 'luxury' items like a P.V array. Mess it up and people are going to get cold or run up huge electricity bills.

This is the problem with renewables and the tariff they offer. Everyone has there eye balls stuck on the financial gain rather than their intended purpose.

As a heating engineer I can see this heading down the same road as the FiT's, and actually see the reasons for the delays.

I think your missing the point
if the the heat loss of a building is 9kw the heat pump will be sized according the area conditions and degree data, If your MCS heat pump installer you will know about the emitter guide that you must show the customer, stating his star rating for property, including this in the quote. The idea of reducing operating temp is to reduce running costs of the heat pump by doing this either install smart rads or oversize rads or LTR's
Most heat pumps only produce 55 degress thats the idea behind the emitter guide and altering RADS

 

[jason121]

All you need to do is size the heat loss in the property using the u values of the house, there is a spread sheet on the MCS web site and webminar explaining all about it,this gives you a estimated guide of the running costs and sizing of heat pump. Next step would be sizing radiators rooms.

 

[FB.]

This is the problem with renewables and the tariff they offer. Everyone has there eye balls stuck on the financial gain rather than their intended purpose.

As a heating engineer I can see this heading down the same road as the FiT's, and actually see the reasons for the delays.

My view on FiT's is that they should be used to get a renewable technology established as a result of larger numbers of installations leading to knowledge, experience, economies of scale and cost savings which subsequently bring the costs down for everyone else.,
But the FiT should not be so generous that people can retire on it!

So someone like me - soon in need of at least a new boiler and ideally a redesigned heating system - could be persuaded to help a budding industry if the cost or benefits of ASHP stack up well against fitting another gas boiler.
If ASHP works out only fractionally cheaper than gas, I'll take it, whether subsidised or not. The subsidy will simply help to kickstart things. Let's just hope that if prices come down (as was the case for solar) that they don't leave FiT's too high for too long which results in another boom-bust.

 

[jason121]

PAGES from the consultation paper
Option 2: Varying RHI Tariffs for Heat Pumps so that they are Linked to the SPF Measured in the Metering and Monitoring Service Package.................................................................................. 71

Option 3: Introducing a Higher Seasonal Performance Factor (SPF) for Heat Pumps as an Eligibility Requirement for the RHI .............................................................................................. 72

 

[jason121]

218. As set out in Chapter 3, the EU sets minimum performance standards for heat pumps for them to be classified as renewable (articulated as a Seasonal Performance Factor (SPF)), and we intend to use a light-touch approach to enforce this by monitoring the Temperature Star Rating of the systems being installed. If installers are intentionally designing systems to perform poorly, we would take action to prevent them doing this. However, in order to ensure that heat pumps are performing as well as possible we could introduce a minimum level of performance that goes beyond what is required in the RED. For example, we could require a minimum SPF of 2.7 as an eligibility criterion. This could be based on the likely design space heating SPFs in the Heat Emitter Guide for Domestic Heat Pumps, which is part of MIS 3005, the MCS installer standard for heat pumps. Setting an SPF of this level is higher than the current EU minimum, which changes every year but is currently 2.5. However, it is lower than that claimed by many heat pump retailers and significantly lower than the SPF levels required by the Heat Pump Stimulus Programme in one of the EU’s largest markets for heat pumps – the German Federal Environment Ministry’s Marketanreziprogramm – which requires 3.5 for air source heat pumps and 3.8 for ground source heat pumps.

 

[sambotc]

F.B you may not require a full re-design if you opt for a gas boiler replacement but without seeing the system it is hard to tell what is wrong. You would almost certainly require a full redesign if you opt for a heat pump as all the radiators will most likely be undersized. If I remember your house is of fairly new construction so the radiators are unlikely to be over sized unless recent additions such as cavity wall and loft insulation have reduced the heat loss. Even then I would think not by enough in most rooms.

i couldn't tell you what the heat pumps reliability is like, it is fairly common technology as said, but my fridge doesn't run 24/7 it cuts in and out depending on temperature, and given its well insulated construction, this isn't all that often.

when you look at carbon reduction, somewhere around a cop of 2.5 will match that of a gas boiler so in theory an air source heat pump could reduce carbon when compared to gas, but in practice this will drop as the days get colder so depending on outside weather factors you could very well find swapping from gas to a heat pump is counter productive in these terms especially taking into account the pasteurisation cycle.

dont get me wrong the technology works and could be excellent in the right circumstances, but in my opinion replacing a gas boiler, or being able to claim rhi in doing so is wrong.

 

[The Solar King]

Why not go the whole hog and install a GSHP? At least that way you minimise the issues of performance as ambient temperatures fall away in the heating season. I have yet to be convinced as to the efficacy of ASHPs, they are after all little more than the back end of an air conditioning unit. Once the investment is made in a bore hole or ground array, it is there for good. It's cost needs to be considered over a far longer period than the heatpump itself. Cost can be a barrier which is why ASHPs are currently more popular.

 

[FB.]

F.B you may not require a full re-design if you opt for a gas boiler replacement but without seeing the system it is hard to tell what is wrong. You would almost certainly require a full redesign if you opt for a heat pump as all the radiators will most likely be undersized. If I remember your house is of fairly new construction so the radiators are unlikely to be over sized unless recent additions such as cavity wall and loft insulation have reduced the heat loss. Even then I would think not by enough in most rooms.

I made a sketch for a plumber/heating engineer friend of mine. It'll give you lads a real-world "case study" to practice on.
See pic below. Radiators marked in orange, with approximate dimensions of the rads in feet to the right of the plan (3.3ft to a metre for those young 'uns among you).
Edit: ceiling height 7.5ft (2.3m).
Also shows "typical" "average" temps in each room, with the lounge at 21'C. With changes in wind direction the lounge can go up or down 0.5'C and the diner will do the opposite (e.g. 20.5'C lounge and 23'C diner or 21.5'C lounge and 22'C diner).
Heat-up time is about 1'C every half-hour. Lowering the dining room rad to balance with lounge makes this 1'C every three-quarter-hour.

Note undersized lounge radiator.
Note North-West-ish-facing front of Lounge which gets less sun and catches more of the UK's prevailing wind (wind direction can change room temp by 1'C).
House is detatched and in a rather open landscape.
Walls are regular brick cavity, dry-lined. Unsure of wall insulation as my old house (built slightly earlier and in a nearby street) had blocks of fibreglass slipped into the cavity (we found this when we had a window changed to a patio door). We don't know what's inside the cavity of our current house.
Loft has about six inches of insulation, which is covered by loft boards (so probably acts a bit like a cavity).
Also note issues with drainage for adding a condensate outlet due to kitchen door and position of drains.

 

[Earthstore]

There may be another reason why your lounge is colder, the rad is under the window, I am aware this is common practice however when it is hot it has no thermal mass above it to hold the heat (no brickwork just a window), all the other rads will warm up the wall above the rad acting similar to a storage heater.

I would just like to simplify this thread for some reading, because due to more government rules it may sound like rocket science to some.

The temperature you are trying to achieve is around 20 degrees, a gas boiler would run at around 65 degrees, taking into account some system heat loss your rads would be around 55 degrees.
If you change to a heat pump they run at lower temperatures, so to maintain the 20 degrees you require you need to have reasonable insulation, the less heat you let out the less you have to put in, also to warm the rooms from cold you would need a larger surface area of rad to heat the same room space because they would be running slightly cooler, still a long way from the 20 degrees you are trying to achieve though.

I have seen several different heat pump systems here in the UK, and most are working very well, some had initial problems but this was due to install plus fine tuning as they are quite complex, sadly the worst one is a local authority house, installed by people that do not understand how they operate so the plumbing/wiring was all quite shocking really.

As to the running costs, I can give a direct comparison here, two friends of mine have similar houses, one is slightly older and uses oil to rads, heating costs £2500 per year, and it is not too warm in there.
The other house is new, well insulated, underfloor heating and a ground source heat pump fitted, heating cost £900 per year, and it is very warm in there. The system was not without its problems in the first 6 months though but well worth the hassle.

The advantage of an ASHP is that it stands outside and if you choose the right make they are very quiet, but for a GSHP you have the added cost of installing your ground collector, whether drilling or laying a grid, plus the inconvenience and mess, you will also need a plant room to put the heatpump and associated hardware.

So normally, not always but normally, ASHP is best for retrofit, but GSHP is best new build.

One other thing that I would recommend, is to have your property surveyed with a thermal imaging camera, but by someone that knows what they are doing, it is a fantastic way to find out where the heat is escaping from your property and some of the remedies may not be too expensive.

I hope this helps.

 

[FB.]

There may be another reason why your lounge is colder, the rad is under the window, I am aware this is common practice however when it is hot it has no thermal mass above it to hold the heat (no brickwork just a window), all the other rads will warm up the wall above the rad acting similar to a storage heater.

Yes, the lounge rad is the only one sitting under a window. It is also under-sized, and apparently the lounge ought to have been fitted with two smaller rads to spread the heat more evenly rather than all at one end. The lounge rad faces the diner, but the dining rad is at right angles to the lounge.
The rads in the rooms other than the lounge are about correctly sized - both in theory and in terms of their ability to heat their rooms adequately.

The temperature you are trying to achieve is around 20 degrees, a gas boiler would run at around 65 degrees, taking into account some system heat loss your rads would be around 55 degrees.

Yes, I once stuck a thermometer on the rads and they get to a little over 55'C on the outside and probably 60'C water inside.

 

[jason121]

could do with a few more measurements like windows and hall and clock room dimensions but here goes
Dining room 1213 watts loss
Lounge 1496 watts loss
kitchen 936 watts loss

 

[sambotc]

What outside temperature is that based on jason121?

F.B do you have a fire in that chimney? Sometimes the specifiers took into consideration other heat sources and believe it or not reduced radiator sizing on the presumption the fire would supplement.

as jason121 has said, more info needed to be accurate. floor construction, windows sizes and materials. Is the fireplace in use? does if have a throat/chair birck or is it open?

 

[jason121]

-3 didnt spend a lot of time on it just did a quickie

 

[FB.]

What outside temperature is that based on jason121?

F.B do you have a fire in that chimney? Sometimes the specifiers took into consideration other heat sources and believe it or not reduced radiator sizing on the presumption the fire would supplement.

as jason121 has said, more info needed to be accurate. floor construction, windows sizes and materials. Is the fireplace in use? does if have a throat/chair birck or is it open?

Yes, the black block on the left of the lounge is a chimney. It is not open at present in order to reduce draughts in the already-cold lounge, but we do open it up and use it at Christmas for effect.
There is an unused (never been used) gas point beside the fireplace, so that a gas fire could use the chimney as an exhaust.

Floor is concrete (house sits on about a 6ft thick concrete raft), with carpet on top of the floor.
All windows are double-glazed, wooden frames.
Diner has 1.8m wide x 1.9m high (6ft x 6.5ft) double-glazed, full-glass, double patio doors.
Lounge has a 1.8m wide x 1.3m high (6ft x 4.25ft) double-glazed window.

 

[FB.]

-

Mmmmmmm a lovely open fire at Christmas. :carolers:




Just don't tell the CO2 inspectors.

:behead:-


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