 | Home > Off Topic > Air source heating. Any feedback? |
 
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315   
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Hi camelman, so if I understand it correctly, your 21Kw GSHP can go though 70kW in a day?
Our peak rate electricity is £0.12 a unit, so if I had a 17kW air source unit that probably isn't as efficient in conversion as your GSHP, I could be looking at a similar electricity consumption  0.12 x 70kW = £8.40 per day.
I guess that is worst case though through the winter. When I was studying the Grant ASHP installation instructions today, I saw that their controllers could support off peak tariffs and increase the water heat store temperature whilst running on the lower night time Economy 7 tariff we have. That would seem sensible, although I guess it tends to be colder at night, so the efficiency of the unit will be reduced. It's on my list of questions for when the survey team arrive. I need to keep the Eco 7 tariff to feed the electric Aga which works on an overnight storage cycle. |
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5th Jan 2021 7:24pm |
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| camelman Member Since: 27 Feb 2013 Location: Peak District Posts: 3368
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Yep, will easily do 70kwh on a cold winters day.
Economy 7 tariffs always have a sting in the tail depending on how your usage profile looks like. The 'day' rates can be double what you'd pay on a flat rate tariff so you have to squeeze as much of your usage into the off peak 7 hours (midnight to 7am usually) to make them worth while. As an estimate of the electricity cost / usage, take how many litres of oil you use in a typical year. Multiply by 10 to get a indication of how many kWh that equates to. If your ashp is quoting a Cop of 4, divide the kWh figure by 4 to work out roughly how much the ashp would use in a year. The above is rough and ready but proved quite accurate when we moved off oil onto the ground source pump. |
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5th Jan 2021 7:47pm |
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| Rashers Member Since: 21 Jun 2015 Location: Norfolk Posts: 3484 
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This is why when we design new buildings the first thing to do is to make the insulation effective and air leakage or permeability as small as possible. New houses have mechanical ventilation and heat recovery units in them to extract stale air and bring in fresh which is tempered by the heat from the stale extracted air. If not they would be terrible and unhealthy to live in. The idea is to heat the building up and keep the heat in. Passivhaus is a design where heat requirement for a dwelling is minimal.
Sadly our housing stock comes nowhere near this level so we spend shed loads of money heating our homes!! It’s worth saying that these units are driven by inverters so their compressors will ramp up and down as required so the max electrical load isn’t a norm but the exception. Well unless you live in an extremely cold area and your home leaks heat like a sieve. Personally, I think building fabric should be your first thing to sort out - if you can. Old properties especially those which are listed, are very problematic in trying to achieve this! No point trying to save energy if you are just losing the heat out of ill fitting windows and doors. Your heat source will also need to work a lot harder thus wearing up quicker. |
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5th Jan 2021 8:10pm |
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315
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Thanks camelman, I found that conversion factor earlier today when I was looking at the kW equivalent of a litre of kerosene.
I was doing exactly the calculation you suggested. Just trying to estimate how much the immersion heater uses as we run that through the summer on Eco 7, with a 2 hour boost around tea time ready for baths, etc. And it stays on the same programme through the winder due to us running the oil boiler as little as possible. The immersion would also be redundant if we moved to a decent ASHP system as well, so another saving. Our current Eco 7 usage by kWh is 62% night, 38% day due to the Aga recharging overnight. It sits on a 30 Amp feed. We also run the washing machine and dishwasher at off peak times as well. So currently, an Eco 7 tariff seems to work well for us. Because of the cost of oil, we only tend to run the boiler in an evening through the winter for 5 hours or so. So often the house is cold. Now I am retired and my wife will be soon, we are going to want heat throughout the day. So we aren't really comparing apples with apples, if they calculate an electricity consumption for the ASHP running pretty much 24/7 through the winter and at a background level in the summer. I am expecting their calculation to say we will use more electricity than our current oil spend, but once I eliminate the immersion heater and a couple of electric underfloor heated bathroom areas, I am hoping it won't be a great deal more. And quite often we will switch on 2kw fan and oil filled radiators during the cold days when we are at home, so again, they should become redundant. Can't wait to see the calculations and to then critically analyse them. As per my earlier comments, I also need to factor in the fact that the ancient oil boiler is unlikely to last another 7 or 10 years so there a cost in the pipeline to sort that out anyway. |
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5th Jan 2021 8:13pm |
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315
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Agree Rashers, due to the age and design layout, the building is like a leaking sieve when it comes to heat retention.
Whenever we have needed to do work on it, we have always tried to improve the thermal efficiency, like better quality double glazed windows and Kingspan insulation underneath the roof felt when we had it re-roofed. We also put a lot more insulation down in the loft spaces and went on a crusade to eliminate draughts from window and door gaps. I've seen what can be done with well designed eco friendly heating at the club where I sail. The clubhouse was a new build 10 years ago, but uses a large Dimplex commercial GSHP in conjunction with hot water solar panels. The whole club house, including the changing rooms and shower areas has wet underfloor heating, set up in 8 different zones, each with its own thermostat control. Brilliant system. Always warm and plenty of hot water for the showers. The only time the twin immersion heaters kick in there are for the weekly legionella boost. If I was starting a new build for myself, I'd willingly invest up front in the best possible insulation and systems to minimise running costs. It's a no brainer to me. |
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5th Jan 2021 8:24pm |
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315
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Sadly, it looks as though an ASHP solution is not going to be cost effective, even with the Govt RHI grant
After the detailed survey on Wednesday they have concluded that we would need two 12kW units. The single 17kW unit they were originally hoping would be adequate would be under capacity. And they said it would need a 3 phase supply which we don't currently have. They even said themselves that they didn't think it would be of interest to us due to the extra capital cost and the fact that the RHI grant is capped. So I don't think they have tried to upsell something to us that isn't needed. So back to Plan B. Stick with the old oil boiler until it fails big time and then replace with a more efficient oil boiler, and/or see what's changed on the grant status when it does fail. Meantime, I'm going to try optimising the radiator water flow by balancing all the radiators and look at the pump speed so I can get the right temperature differentials between the flow and return. Also going to try running the heating 24/7 for a period of time with a lower night time temperature to see if that's more cost effective than starting with a cold house every day at 4:30pm and warming it up until 10:00pm then switching off. If the boiler does run 24/7 I should also be able to eliminate the immersion heater which from what I can gather is probably costing around £500 a year in electricity. |
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8th Jan 2021 3:20pm |
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| Rashers Member Since: 21 Jun 2015 Location: Norfolk Posts: 3484
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That’s a real shame
I am glad they were up front with you. I was worried as ASHP are the new double glazing of the 70’s and there are some bonus hunting sales reps doing the rounds. I would now seriously think about changing your boiler. Our new boiler made a real difference to our heating Bill. They are very efficient compared to the old ones. We removed a 25 year old Potterton and fitted a Grant. Went for a pressurised system so we get a far better hot water flow  |
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8th Jan 2021 3:47pm |
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| LandRoverAnorak Member Since: 17 Jul 2011 Location: Surrey Posts: 11324
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Sorry, wrong thread
 Darren
110 USW BUILD THREAD - EXPEDITION TRAILER - 200tdi 90 BUILD THREAD - SANKEY TRAILER - IG@landroveranorak "You came in that thing? You're braver than I thought!" - Princess Leia |
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8th Jan 2021 3:51pm |
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| camelman Member Since: 27 Feb 2013 Location: Peak District Posts: 3368
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Did they make any reference to inverter driven ASHPs?
Our ground is 21kW running on single phase. AS it's inverter driven you don't get the huge surge in power requirements when it kicks in and out so doesn't need 3 phase supply for that output. I can only think that the 2x12kw requirement, even with an inverter would take it above the single phase supply limit? |
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8th Jan 2021 3:53pm |
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315
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Hi camelman. Yes, the Grant units are inverter based. I did wonder if it was because of the power surge if both units kicked in together.
Just had the boiler controls in bits again to remind myself of the wiring as thinking of fitting a Hive thermostat to give me more control over the day time and night time CH room temperature settings if we trial running 24/7 for a while. I'll resurrect the old topic on smart thermostats to ask a few questions on Hive installation!! Thanks again to you and all the others who provided input on ASHP. |
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8th Jan 2021 4:41pm |
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| camelman Member Since: 27 Feb 2013 Location: Peak District Posts: 3368
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Did you look into biomass at all? They are a bit more expensive but have a higher round grant.
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9th Jan 2021 10:40am |
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| lohr500 Member Since: 14 Sep 2014 Location: Skipton Posts: 1315
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Will take a look camelman. Certainly worth investigating.
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9th Jan 2021 1:04pm |
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| camelman Member Since: 27 Feb 2013 Location: Peak District Posts: 3368
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The pellet boilers themselves are quite compact, just need enough space for the hopper. They get delivered in a tanker just like oil.
Just looked at the current rates and the biomass payment is similar to ashp at 7p/kwh so the grant would be c£10k over the 7 years. |
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9th Jan 2021 1:14pm |
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| Rashers Member Since: 21 Jun 2015 Location: Norfolk Posts: 3484
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There are biomass boilers which are just filled by the sacks of pellets rather than via a hopper. In this case, the pellets are delivered on a pallet and you need somewhere to store them (just like coal). You then go and fill the boiler up as and when.
A word of caution. Biomass in the industry has fallen off the side of a cliff. About ten years ago every man and his dog were fitting them. Commercially, I knew more biomass boilers which stand unused than used. The biggest I have saw was under Stansted Airport in Essex where the biomass was delivered once every two days by artic. Our local Sainsbury's has one, but saying that, I can't remember the last time I saw the boiler hopper being filled. They were mostly fitted in conjunction with Gas Boilers to satisfy the planning / building regulations and after the buildings were signed off, they were generally never used again and the Gas Boilers reconfigured to run the buildings. You need good quality pellets which are very dry. Damp pellets will stop the boiler from working and once you have a shed full / hopper full, it's then too late. We know a lady in the next village who had one fitted about 8 years ago. She is delighted with it, from a heat / cost point of view but when she rebuilt a farmhouse a few years latter, she decided against installing one. The reason she gave was the constant filling of the boiler / lumping bags around (as the pellets were usually via a roadside delivery only). Oil was easier and less hassle. If you do go this road, work out how long the boiler will run without the need of human intervention. It's not like a gas / oil boiler which you set the thermostat to 18 degrees and then fly off on holiday for a fortnights skiing (if you can still remember those days). Biomass (along with combined heat and power units -CHP's) are also now not seen as such a green alternative as it is still burning something to create heat. They also need regular and quite specific servicing. I used to work for a reasonably large facilities management company. We had probably thirty combustion engineers, but only one of those was qualified to service biofuel boilers. He was stacked out of work originally, but we just found that people became disenchanted with them and they were mostly turned off and never used again. Scandalous as most had been fitted with large Government grants and a large proportion were in public buildings like schools and colleges. |
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9th Jan 2021 2:58pm |
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