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Author Topic: Nervous about ASHP  (Read 3279 times)
Countrypaul
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« Reply #30 on: June 10, 2018, 09:10:20 AM »

Do you have any sort of loading valve on the stove such as a Laddomat or Esme? Using a stove with backboiler that does not make use of a laoding valve can result in very poor stove performance, there are several threads on this subject if you want to read more about it. The usual results due to lack of loading valve appear to be radiators never getting properly warm, excessive tar and soot production and the house always feeling cold!  Two other factors that can contribute to poor stove heating are gunked up pipes, try powerflushing the system (this will apply regardless of whether you reply on the stove, oil boiler or ASHP), and not having the lockshield valves on the radiators set properly (again there is a recent article about that).  Obviously this won't help with your flick a switch and have the heating come on, but might improve the stove and radiator performance significantly.  Are there any pums/valves on the stove circuit to direct the hot water to the DHW tank or central heating?

What make/model of stove is it you have? Some you can take the boiler out of, others you can't is my understanding. Have you thought about combining the stove and oil boiler using either a thermal store or neutraliser etc. That way you could also get a away with a smaller oil burner (less expensive) which would cycle less, but rely on using the stove if the weather came along with a really cold spell.
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billi
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« Reply #31 on: June 10, 2018, 11:16:47 AM »

exactly CP  ,  first to have a look at the current install , seems  a good  start  to have a woodburning boiler plumped in and   just find a way tro complete   with an add on  heating idea
Billi
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Philip R
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« Reply #32 on: September 25, 2018, 09:13:47 PM »

Just seen this thread.
I would stick with the LPG and go for a Robur K18 Gas absorbtion heat pump. I dont have one as my condensing boiler is working well. But its replacement, wherever I end up living ( if on mains gas or LPG) would be one of these or something similar that enters the market.

Although dearer than electric ASHP, It is a lot more powerful. I also can produce decent hot water output with little decrement to COP, Also electrical load is the air fan and circ pump, not the high powerred compressor. So more realistic chance of powerring it during a possible power cut, using smaller backup power source.

Philip R
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andrewellis
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« Reply #33 on: September 26, 2018, 09:27:27 AM »

Most of what I wrote probably doesn't apply as I didn't notice you are running a wood burner but the same principles apply.  The problem with a stove is it isn't putting out much heat overnight.  Therefore you need more power to play catchup in the day.  We had a 22kw oil burner and now have a 12kw GSHP.  It runs 24/7 keeping the house at 19ºC on average.  Its worth doing the calculations very accurately or you will be sad.

We have an old granite smiddy that was converted in the 80's.  I did similar calculations to yourself but also did a room by room calculation.  You can download the mcs spreadsheet which the installers will use.  To convince myself I also did real world calculations last year by placing an iPhone in the boiler recording audio all night and day for a few weeks.  Luckily the temperature was -6 last year.  I turned the boiler down to its minimum which worked out at an average of about 50 degrees. I also left it on 24/7 with a thermostat temperature of 19 degrees.  I was able to achieve two things then.

a) know if the lower temperatures would work in the rooms with the current radiators.  Some were a few degrees short.  I have added a replaced a few radiators.

b) how much oil was used.  The manual for the boiler will tell you the oil usage per hour depending on the nozzle you have fitted.   Then download the wave form and the on/off periods are very clear.  Just use some audio software to measure the on/off timings and you will get oil usage per hour.     I tried to see the difference between windy and non windy days. I also had a raspberry pi and arduino recording the outside temperature and room temperatures every 15 minutes so I could correlate between oil usage and what was happening outside.  There was a little lag in the house due to the granite heat sink.  Could you record the weight of the wood being used to do something similar.  Approximate the calories per kg and the efficiency of the boiler stove?

In the end I went with a GSHP ( borehole) as the ASHP didn't make sense in Scotland with the colder weather.  The COP at colder temperatures drops off rapidly.  As long as you can stump up the money the RHI will pay for the install over 7 years.  So far its working out well though I am waiting for the first winter to finish.  One thing I didn't take into account is how quickly the house temperature drops when heating the water.  I had wanted a larger DHW tank with the intention of heating water at night to see us through the day.  However we had an integrated tank in the Nibe F2155.  It isn't large enough to see us through the day and ends up constantly topping up the tank temperature after use.  You can adjust the ratio of home vs water heating but we definitely feel a temperature drop.  It isn't entirely a fair setup yet as we have got all our radiators in whilst I finish building the kitchen and living room so it might not be so pronounced an issue later.

As others mention. Insulate.  I did the attics and removed all the downlighters which where effectively 20 x 4 inch holes in to the attic space.   The attic insulation is very cheap and a no brainer.  I also found a lot of mould in the attic.  We had a huge open chimney that was very effective at removing any heat we managed to make.  An extractor fan in the bathroom and a few vents in the tiles has fixed that.  Just be careful about leaving ventilation behind the walls as these old places need to breath.  The walls already had some insulation from the 80s and any time I do some work I am updating the wall insulation.  Before doing all the work even the oil boiler struggled to keep the temperature steady.
« Last Edit: September 26, 2018, 09:38:40 AM by andrewellis » Logged

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Westie
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« Reply #34 on: September 27, 2018, 04:42:31 PM »

Just seen this thread.
I would stick with the LPG and go for a Robur K18 Gas absorbtion heat pump. I dont have one as my condensing boiler is working well. But its replacement, wherever I end up living ( if on mains gas or LPG) would be one of these or something similar that enters the market.

Although dearer than electric ASHP, It is a lot more powerful. I also can produce decent hot water output with little decrement to COP, Also electrical load is the air fan and circ pump, not the high powerred compressor. So more realistic chance of powerring it during a possible power cut, using smaller backup power source.

Philip R

It's a very interesting device. In particular the water temp delivery at up to 65C means the low flow rates of my microbore based CH system should be okay. I wonder what the reliability will be like, IIRC absorption fridges are very reliable as there is obviously no compressor.  Copy of a quote below.. it excludes installation....



* temp.jpg (67.49 KB, 686x559 - viewed 212 times.)
* RR News K18 Press Release W (1).pdf (251.76 KB - downloaded 17 times.)
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djs63
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« Reply #35 on: September 27, 2018, 06:05:54 PM »

The accessories total seems to wrongly added up. Is that correct?
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Philip R
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« Reply #36 on: September 27, 2018, 10:20:02 PM »

Bear in mind that operating the output at 65 deg C will reduce its Cop. Size the heat emitters to run at say 50 / 55 deg C and the cop will be better than at 60 deg.

Absorbtion fridges are reliable.  seen some running older than me. So long at gas heated high pressure parts do not spall or rust, the device should be reliable.

This type of device is available in larger outputs from some of the commercial heating boiler companies.
The K18 is the first small device that can be called domestic. Whence some other companies enter the fold, the price should drop and then it will become the appliance if choice for gas heating, replacing the condensing boiler.

Philip R
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Westie
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« Reply #37 on: October 13, 2018, 03:26:41 PM »

I don't see why this heat pump from Robur doesn't qualify for RHI, I realise it burns gas (or even cleaner LPG in my case) but electrically powered ASHP use electricity from our grid that's still largely generated by gas!  
The vendor says it's because the government (DECC as was) decided they didn’t need to offer a payback incentive because gas is that much cheaper than electricity – and because their advisors are the Heat Pump Association (HPA) which is comprised of electric heat pump manufacturers. I checked the HPA membership and that does appear to be true so their advice to DECC is almost definately biased!
« Last Edit: October 13, 2018, 03:33:02 PM by Westie » Logged

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Philip R
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« Reply #38 on: October 13, 2018, 09:03:38 PM »

Interested that these do not qualify for RHI.in the eyes of decc and hpa, gas driven heatpumps are less renewable than electrically driven ones. How bizarre. Shows the high level of thickness present in these governmental and trade associations. They are backward.

 Look on the upside. It does not need to be installed and signed of at great expense by rhi approved agent / contractor. Have you looked at the economics with and without the grant? Gas and electric. My take on things is that agreements can be broken. I believe fits and rhi agreements may be torn up before they officially expire.
I will check out what Gassafe have to say about which gas ticket is required for its legal connection to the gas supply.

Why do you think that LPG is any cleaner than natural gas?

Philip R
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Westie
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« Reply #39 on: October 13, 2018, 10:10:40 PM »

Re Propane vs NG I see your point, it's arguable.  Propane produces slightly more co2 than NG when burnt but requires only half the volume of gas to produce the same heat. Before it's burnt NG is methane - a powerful greenhouse gas so leaks have a  significant effect , propane isn't a greenhouse gas so leaks don't affect the ozone layer, although because it's  heavier than air it explodes well  sh*tfan
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Philip R
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« Reply #40 on: October 13, 2018, 10:43:01 PM »

Methane is a greenhouse gas because it is lighter than air so floats up to the stratosphere. Propane is heavier than air so cannot rise to stratosphere. Instead it sinks into drains, basements and  dips in the ground. I am careful when i undertake gas work but a more so when doing LPG gas work. Because of its wider explosive range and higher energy density. Recall the Spanish campsite gas explosion of the 1970s.

Your safety justification is like saying you could get run over by walking on the pavement, so decided to walk in the road instead!

Philip R

Propane offers  a higher efficiency compared to natural gas because of higher allowable CO2 concentration in exhaust raises condensation temperature threshold, so boiler condenses water better.
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