For help, advice and discussion about stuff not related to aviation. Play nice: no religion, no politics and no axe grinding please.
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By George
FLYER Club Member  FLYER Club Member
#1848069
Hope this may get some answers!

We have had a survey done and our house roof is well positioned to take 16 PV panels, and the cost should repay itself in 6-8 years. Getting the quote tomorrow and think it is in many ways a no brainer.

There is also the fact that we should be paying considerably less for electricity, so in a roundabout way of thinking, this is better than investing money in a sod all return account too and we will also be able to export the surplus on good days.

We also have a 15+ year old oil fired boiler and it's pretty asthmatic and gobbles oil. So we are also looking at an air source pump to do the heavy lifting of the heating at the same time, as it makes sense to use the electricity from the panels to work around the house as much as possible.

So, I have a couple of questions here.

1. To export surplus you need a 'smart meter' but smart seems to be an oxymoron as you need a mobile signal for it to work. We are with Ecotricity and they would be happy to supply one but they don't have a meter that works off bluetooth to the wifi. They said other suppliers might be able to provide a solution. Anybody got experience of a smart meter that will work where the signal is rubbish?

2. The oil boiler could be replaced with a more efficient modern one, but if we want to be green, it is not really an answer. We don't have the space or budget for a biomass system. So who has experience of an air source pump and what are the benefits?

Over to the experts out there!
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By Morten
FLYER Club Member  FLYER Club Member
#1848120
Air source heat pump = (potentially more but) less warm water, so traditional radiators may not be enough to keep warm. A good installer should be able to do an assessment of whether your existing system is big enough with the lower temperature water. If recent conversion and well insulated you may be OK.
What do you think of the noise they make? It's put me off... If you have the ground you could potentially look at a ground source pump instead which would be quiet. Same temperature issue.
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By Morten
FLYER Club Member  FLYER Club Member
#1848124
Except it is on a lot more of the time, I'd think. To be fair, the low temp has been the killer for us, not the noise, it's just been an issue I've not liked.
By Rallye
#1848134
I have actually a air/water pump,and the noise is really minimum.Also the noise maker is outside and even at 1 m,you ear nothing (I speak about the new pumps).
I have a floor warming with low temperature water and it is perfect.For radiators,i think you need warmer water in the installation.
Concerning my sanitary water (shower,etc...)water is at 40 ° ,higher you need a resistance which consume more electricity (resistance in the boiler).

That's my experience.
Ideal,water /air pump heating by in the floor and solar panels.
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By Flying_john
FLYER Club Member  FLYER Club Member
#1848135
I would add 1 or 2 years to the expected repayment of investment.

My export is deemed at half of my generation amount as measured by the generation meter. I do not have an export meter, not do I have a "smart" meter, and I didn't think it was some "law" that you had to have one.

I would invest a further couple of hundred in an automatic excess production diverter, into a resistive heating element in a tank, since you get paid for the electricity, whether you use it or not, so you may as well use it.

The one I use has two connections to resistive loads, so one is for an immersion heater and one is to an electric underfloor loop. This automatically kicks in if you are not making use of all the power you are producing.

Air source heat pump is noisy, definitely wouldn't want it running at night. So I run it just on sunny days and then only at peak production hours if I am not using the power for something else. You end up with a hierarchy of devices that use the power that you generate. Mine are on Alexa, so I can voice or phone switch stuff on/off.
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By nallen
FLYER Club Member  FLYER Club Member
#1848144
The house I had built in Denmark a couple of years ago has an air-source heat pump -- it sits in the utility room, where it hums away gently, pulling in the hot, stale air from the house and extracting the heat. (I wouldn't want to share living space with the noise but it's fine shut in the utility room; inaudible in the rest of the house.)

The system works very well, via underfloor heating, but the house is very, very well insulated. My understanding is that using heat pumps to drive existing radiators is a sub-optimal solution -- their efficiency drops considerably when heating the water to "radiator temperature".
By riverrock
FLYER Club Member  FLYER Club Member
#1848168
Radiator output is normally rated & sized based on difference in temperature between room and water of 50degC (so you get its rated output if your room is 20degC and the hot water from the boiler is 70degC).
A heat pump loses about 2% efficiency for every degC higher it heats, so the lower the better . They are typically 40% more efficient outputting at 35degC rather than 55degC (examples here: https://www.mastertherm.co.uk/heat-pump-efficiency ) . Much hotter than that (you normally want hot water in a tank to be at least 60degC to reduce legionnaires disease risk) and resistive heaters are normally needed to boost the temperature further.
They also reduce efficiency when environment outside (air, ground) is colder, not working at all when its very cold outside (so back to resistive heaters).
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By rikur_
FLYER Club Member  FLYER Club Member
#1848174
Headlines are: airsource (air to water) heating runs the radiators cooler than a oil boiler. So typically you run them for more (or even all) of the day to keep the place warm.
In a well insulated house this isn't a problem as the thermal losses are low, in a poorly insulated house you are losing heat 24x7 (whereas with an oil boiler you'd just let the place go cold during the day/night). For the same reasons you tend to need larger radiators with airsource (or in a new build, underfloor heating).

That said, oil boilers get less efficient under low load, whereas airsource gets more efficient. In practice most of the year a system isn't working flat out, and quite plausible for airsource to be more cost effective than oil.

We went the unconventional route of air-to-air, which has the advantages that you can control rooms independently and it can provide cooling in the summer. Very happy with this, albeit some lessons to learn on optimising the use of it.

We've found air source inverters to be quieter than the oil boiler. It does occasionally hit a resonance on cold days, but normally not noticeable.

As our oil boiler was still young and serviceable, we kept the oil boiler for cold weather boost.
#1848213
Without wishing to distract the thread, I would be amazed if PV panels would pay back within 6-8 years without subsidies. Especially in Wales!

My 4kW (16 panel) system is ground mounted & points due South and at an optimum angle with zero shading, and even with subsidies I am looking at 8 years break even at best.
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#1848217
I'm glad someone else said it @Colonel Panic. We have had these discussions numerous times over the years and even when the subsidies were much higher I couldn't get the numbers to work. But then I guess interest rates were a little higher then. The marketing literature around these schemes tends to be best case scenario plus 10% every time. They seem to assume 100% efficiency from the panels over their lifetime with zero maintenance. I cringed many a time when people were spending their hard earned in the hope of having a payback in the future, when the biggest risk was whether they would live long enough.
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By George
FLYER Club Member  FLYER Club Member
#1848219
@thecolonel pharpppp! ;)

I have based this on what my neighbour has achieved so far, but TBH if it’s 8 years and a bit, I won’t worry as I want to be a bit greener than I am at the moment. The thought of having a substantial dent taken off what I’m paying for power is enough.

The company have been very honest about projections too but will know for certain when I get the quote in the next few days!