Air Source Heat Pumps

Oil-aversion

Hi,

I’ve been reading avidly and seek your collective knowledge and experience on an ASHP installation. There isn’t gas to our house and the oil fired system while basically reliable is becoming increasingly expensive to run. We have a Victorian stone built barn converted to a single storey 3 bed house in the mid 90’s. It has roof insulation, double glazing with dot and dab plasterboard walls; it is well insulated and in the summer frustratingly retains heat even with the doors and windows open. Heating is through a two manifold under floor wet system that works well if run fairly continuously as described in posts on this thread, the original design was for 14Kw for everything on together. There’s also a very large log burner, 16Kw I think, in the main lounge (unfortunately without a water off take) that can fairly quickly give some heat and through radiation/convection supplement the under floor system quickly modulating the room to ‘off’. Hot water comes off the system at a spot remote to the boiler heating the coil of a pressurised Megaflow tank with immersion heater back up. The roof is overshadowed and isn’t well orientated for solar panels and we’re a bit restricted by the house deeds (and our relationships with our neighbours) to make roof mounted panels or water heaters attractive. Finally I’m currently installing LED lighting to drop the electric demand particularly for those places where the family like them on for extended periods (you know what I mean).

I’ve read through all the posts, yes all of them - engineers are like that, and tried to research all the other ins and outs of incentives and installation requirements. I have in mind to get rid of the oil boiler and oil tank locating an ASHP where the tank formally sat. It’s in a good spot where limited fan noise wouldn’t affect us or the neighbours. There’s an easy pick up to the flow and return legs of the water system and convenient for power and control connections. Those I’ve talked to suggest fitting a new water tank local to the ASHP. I would prefer not to have to chop the house round, there’s no loft space and running new pipes or cables wouldn’t be easy or aesthetic. I am thinking of a ASHP that runs at 55 to 60C directly replacing the functionality of the oil boiler to feed the water tank coil with the under floor heating diluting its temperature down as it does currently. Alternatively it sounds more efficient to run a system at a lower temperature around 30ish for the under floor with hot water provided by the existing immersion heater lifting the temperature from the ~30C provided by the heating coil to 60+ . This has the attractiveness of not have to change anything around the water tank, it is well embedded into the structure - but it would consume more electricity. What do you think of this proposal?

What I’m not clear on is how much of this I could do myself. Pulling out the boiler and oil tank plus mounting the ASHP doesn’t look technically challenging including the drainage and plumbing. I know electrical installations have to be competently done, inspected and signed off. Is there an equivalent requirement for the plumbing side? Does this have to have planning permission and be checked for Building Regs? And presuming I can buy the ASHP unit myself (I see 13Kw units quite economical on Ebay) and install it myself would that make RHI, EPC and FIT’s difficult? Would the units MCS certificate be enough or do I have to have it installed by a MCS accredited installer (with a consequential escalation of cost)? And have I missed anything else relevant?!

A long post, sorry, with quite a few questions that boil down to; are my thoughts on what to do OK and what approvals and regulation do I need to fit in with?

Thanks in advance for your views and opinions.

albyota

Hi, what temperature is the under floor heating thermostatic valve set at?
Do you know what centers the under floor heating pipes were installed at, I.e. centre to centre?
Yes you can buy a heat pump yourself, but buy good quality, or buy a cheap one this year replace it next year.....!!!!
If you don't get it installed by an MCS installer, you won't get the RHI.....if it ever happens, ( I've been waiting 5 years). If budget will allow, go for Mitsubishi Ecodan or Panasonic Aquarea.

Hope this helps

Oil-aversion

Thanks for the reply Albyota;
System stat is set to 45C but will go down further.
Pipe spacing is 20cm on the installation drawings, I presume they're pretty close to that, there does seem to be an even temperature spread to stockinged feet.
Thanks for the steer on good units to deploy.

So I could go it alone, ignore all the incentives and just save money on oil?

matelodave

You would have to use a MCS installer to qualify you for any of the incentives.

I'd be wary of buying a cheapie and hoping that it would do the job, you might be quite disappointed. Mines a Daikin 11kw split unit, cost just over £6k including installation & commissioning (hot water tank was extra)

Where is your present boiler located, you might find it easier to install a split system rather than a monobloc. A split system has the compressor unit outside the house and an indoor hydrobox which incorporates the heating circuit to refrigerant heat exchanger - it's easier to have long runs of insulated refrigerant piping between the two units - quite long runs (75' comes to mind). You'd need an refrigeration or a/c engineer to connect it up though as the system has to be gassed properly otherwise you'll damage the compressor

Whereas the heating circuit has to be fed outside into the monobloc unit which can make it more difficult if you can't get the unit close to the house and you have to be mindful of the possibility of heating water freezing.

Ideally you want to run the heating circuit at about 30-40 degrees to get optimum efficiency. Most COPs are spec'd at 7 degrees outside to 35 degrees inside so you should do a few calculations to see if your u/f heating will adequately heat the place at that temperature. If you run it much warmer than that then your COP will suffer.

I run my system at a nominal 30 degrees but the flow temperature is adjusted depending on the outside temp (flow temp is +25 when its +15 outside, and +42 degrees when its down to -5) The max temp it can get to is 55.

You can get high temperature systems which usually have two compressors to run flow temperatures at 60-70 degrees which could be an option although I don't know what sort of COP they've got. You could try turning your mixing valve down a bit to see how well your present underfloor system copes with lower temperatures - you might be able to save a few bob as well

Regarding your hot water tank temperature, do you really need to keep it at 60, we manage with ours at 45 with a weekly boost to 60 to sterilize the tank. 45 is hot enough to shower and general use. washing up & the washing machine are cold fill and heat their own.

Electrically they aren't all that complex, ours has three fused feeds 1 x 32a for the compressor unit, 1 x 32a for the 6kw back-up heater and 1 x 16a for the hotwater immersion (which does the 60 degree sterilisation) Then there's just the controls, room stats and a motorised diverter valve for hot water or heating. The room stats control the u'f heating circuits and circulating pump.

PM me if you want more info

albyota

200mm centres may mean you have to run the heat pump nearer to 40 degrees, but Yep, go it alone, give me a shout if you need some good free advice.

AL

deano72_2

I'm no exspert generally on ASAP, but from the 260 installs iv seen on a new build site im not overly impressed but to be fair it's not all down to the heat pump it's self.all the builds are new build with UF heating so I can only comment on this paticular site.
Before even thinking of installing you got to have all the basic boxes ticked.
1.insuallation insulation as many have said on here before.
2.everything needs to air tight, the new builds iv seen was tested and im not sure how they passed as you can feel the drafts from the patio doors/front doors
3. So,assuming the house is squeaky airtight then by rites you will need hru (heat recovery unit) for air movement
4.design is critical.rite tool for the rite job
5.someone who knows how to correctly install it and commission it.don't just flick the switch and say there you go,!
6. Be realistic of its performance, people coming from there nice hot rads to touch to hardly feeling it on your feet or not feeling it at all if it's installed between the floor joist maybe disappointed.
7.understand how to fully operate the system.

I was going to try think of 10 but starting doze off a bit here so sure there's something i have missed.

So once you think you got a nice cosy insulated airtight house hire a infrared heat camera to pick up any spots you may have missed.

From what iv seen a lot of these occupants have harendous bills, now that would be unfair of me to point the finger of the ashp as I don't live in one the houses ...

Would I have one in my 1930s house? No chance
Would I have one in a new build? For sure, as long I was the one doing the build and knew it was tight as a ducks ar55

Mousecatia

Hi all,

I live in a village with no mains gas and rely on oil for the heating and hot water.
The house is a semi detached with radiators and a wood burning stove in the lounge, the oil burner resides in the garage and is on its last legs.
I was considering having a ASHP(air source heat pump) fitted along with PV panels to supply electricity to both the house and the grid and solar panels on the end of the house to compliment the ASHP and running a non vented heating/hot water system.

Having read the reviews on what I thought was the best ASHP (mitsubishi ecodan) and its issues with icing up and noisy fans, I dont want to antagonise the neighbours, I am now thinking of burning more fossil fuel and just updating the oil burner.

Any suggestions would be happily received as to which direction to go in.

Cheers,

Rich

matelodave

Solar PV won't help much with a heat pump - the pump runs mostly during the evening and mornings and in the winter when the days are short and the sun doesn't shine.


Despite what you might hear, they really aren't all that noisy. An oil fired central heating boiler makes more noise - most of the criticisms are from those who have never had one but know someone who does!!!!. Likewise they only ice up if they aren't configured properly, ours does get frosted but it defrosts OK, even when it's been down to -14 (the lowest I've measured in 3 years where we live)

I would think that you'd be better off replacing the knackered oil boiler. The radiators won't be sized to suit a HP so they would all have to be replaced. As you've already got an oil tank etc the cost would be just for the replacement of a boiler.

danridesbikes

desperately looking for a plumber who deals with these in Lincolnshire, can anyone point me in the right direction?

thanks

matelodave

Probably the last bloke you want is a plumber - if you are interested then you'd be better off having a look at the MCS website and talk to an accredited installer - http://www.microgenerationcertification.org/consumers/installer-search


At least you should get someone who knows what they are talking about and will be able to do work to specific standards