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Author Topic: Help and advice needed Please, Biomass DH costing a fortune to run  (Read 30568 times)
Martin0121
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« on: January 28, 2014, 04:31:49 PM »

Please bear with me on this, it is a very long post with lots of problems and questions.  Any help or advice would be greatly appreciated!

In essence, before you start reading all of this, my questions are:

Is it normal for a biomass district heating system to be less heat efficient than Oil?
is it normal for it to take an age to heat the rads and thus the house?
is it normal for the rads to never get properly hot?
is it normal for the rads to not turn off?
is it normal for the cost to run in a house to be higher than it was with oil.
is 0.05 per kw normal?
Is there anything we can do?

We live in on a farm estate in Scotland where the Landlord has converted all of the heating from Oil to a Biomass wood chip fed system.  The biomass boiler is situated in a barn and feeds 7 houses.  (I however only have info and knowledge for 4 of the houses, the 3 in my terrace and one adjacent).  The system was installed in November of 2012 and from the out set there was problems galore.  Problems which cost the landlord at least one tenant due to the inefficiency and cost of the new heating.

In August 2013,  I moved in to the 3 bed end terraced house that that tenant had moved out of, and being made aware of some issue with the heating I set about trying to figure it out.  The landlord had quizzed the installers and service engineers endlessly over the issues and had been told that there was nothing wrong.  This issue was that when the individual heat exchanges in our houses were off, the meters were still accumulating charges.  To cut a long story short i contacted manufacturers and figured out that when the exchanges were installed and tested, the installer failed to remove the giant red tag from the flow vale that said remove before use. This resulted in all of the houses flow valves being open and the heat exchanges thinking they were on full power 24/7 even when they were off.  The installers are still taking no responsibility for this even though this was an ongoing problem for about a year.  That is now resolved but am telling you in case the extra load on the system may have a contributing factor to the current issues.

The current issue is that to keep any of the houses to an acceptable temperature we all have found that the heating needs to be on for such a long period of time to heat the radiators up to an acceptable temp (I am using 19C as my target) and they have to stay on for several hours to heat the rooms, that it is costing an absolute fortune, close to 250-300 per MONTH. The Landlord charges 0.05 per Kwh + VAT. The rads in the houses never get HOT, they get warm but not so hot as to not be able to keep your hand on them.  Rads with TRVs do not switch off, even if they are set at frost protect for rooms that we do not need at 19c.  The heat loss in the houses, so far as I can tell, is no worse than most, at about 1c per hour.  The landlord has gotten to the point that he has asked me to do some experiments on the empty houses to see if i can help him figure out the problems, so I have some data to show.

But there are some more things that i should probably tell you: of the 4 houses I am looking at, there are 3 different systems between them.

The first house, a bungalow, has no heat exchange, instead it has a water storage tank in the livingroom which fills from the DH system, it measures its units used in Mwh but also shows its current energy use in Kwph. Its junction box and meter are on the outside of the house in a cabinet.

The next 2 houses are in the terrace, a 3 bed and a 1 bed.  Their junction points are also on the outside of the houses in a cabinet with a Danfoss Heat exchange, a gundfoss Alpha2 pump and metered in Kw and Kwph.

The last is my house, I also have the Danfoss exchange and Alpha2 pump but mine is located inside my house in the utility room.

Using my house as an example before i give you more in depth data for the 1 bed:
We have 12 rads all have TRVs, there is no central thermostat.  We have all but 5 of the TRVs set on frost protect only. The 5 that are higher are set between 0.5 and 1 (out of 5 points), these are the Utility room, the kitchen, the livingroom, a small room between the kitchen and living room, and our main bedroom.  these settings give these rooms a max temp of 16 (found through prior tests).  we have all the downstairs set so low as we have found it much more cost effective to use the 2 log burning stoves to heat downstairs to higher temps.  As at these current settings, while running the heating for 1.5 hrs in the morning (getting out of bed) and 1.5 hrs in the evening (before going to bed) it is costing us 60 per month, and another 60 per month in logs for the fires, which i light every day at approx 2pm and stop stoking at about 7pm. This heats our downstairs up to about 22c if we let the heat flow through and up.  OK 60 on the biomass heating isnt the 250 that I said earlier but that is because i work from home and am able to do the log fires.  Using the heating as is, none of the rads get anywhere close to their TRV temp and never turn off, our exchange registers readings of 330 litres per house flow, 72c input temp, 42c return temp and 15kw per hour usage on average.  If we were to run the heating for a length of time suitable to get the house up to an adiquate temp with out using the log burners we would be in the 250-300 range ( again previous tests showed me that we would need to run the heating 16-24hrs straight to get up to 19-20c, and even then the TRVs dont really shut off.)  This brings me to the other 2 houses;

The other 3 bed is showing 250 per month bills as they are a 9-5 working couple  they have to set the heating on so much and so long to maintain the temp.

The 1 bed is where i have most data, I hope someone can make heads or tails of this, its average use while on (aiming for 19c) was:
From starting air temp of 13c at 1pm, 249 litres per hour flow, 76c inc flow temp, 48c return temp, kwph use of 8.3 it hit 19c after 9.5hrs with a flow of 254litres per hour, inc temp of 76, return temp of 50 and Kwph use of 7.6.  Now to get to this is took 9.5hrs and used 74kw of energy which is 3.70 not inc vat.  I left the heating on all night to even out the house and try to give the place a fairly constant temp, as if it was lived in, the next day at 12 mid day i went back to find the house at 22c flow rate of 47 litres per hour, 71c inc temp, 50c return temp, only 1kw per hour usage and all the rads were still on warm (confusing that they were still on / warm) this had used 95kw over night, 4.75.  anyway, i turned all the rads DOWN to 2 and came back at 2.30, only 2.5 hrs later. it had gone down to 20c  in the house but the flow rate was up to 118 lph, the inc flow temp 74c, return temp 42c, kwph use was 4.2, 3 out of 7 of the rads were off, properly cold - but it had used 10kw of energy (0.50) whilst cooling down from 22c to 20c, now i am confused!  i then turned it all off as i wanted to simulate being away for 3 hours (so no need for heat), i came back at 7.45pm the temp in the house was 16c all the rads were stone cold, great middle range starting point, put the heating on came back 2hrs later and it was 19c, bingo!, and had only used 10kw to do it, 0.50, and again 3 out of the 7 rads were off.. Ok bed time, all heating off, timed to come back on at 6am for 1 hr, came back to find the house back down to 13c when i was able to check it at 1.30pm, having used again only 10kw for that hour in the morning, i had set the timer for another hour at 2pm but i just put it on full and as of 4pm the temp is still only 17c and it has used about 30kw.

I know this is a lot of figures all over the place but i hope someone will know what they mean.

I have no experience of the oil heating in this house but from what i have been told by the people in the other 3 bed is that the oil was very hot and efficient, even before all the houses got fully double glazed!   The last house we lived in was also a 3 bed, semi, with no double glazing, old rotten doors, draughty sash windows, very poorly insulated and had a 9 year old oil boiler which leaked oil, driped oil into its burner instead of spraying it which created black soot on the walls and flue, so all very inefficient, but it only cost us 100 per month in oil for the winter months and we were always warm.  Here without the log burners we would be freezing or skint.

I can provide images of anything you want and typed data sheets from my previous tests on my house and boiler if they would help.  

I wont even start on the data for the bungalow with the tank as it constantly runs at 8.5 kwph no matter what, and still wont get warm.

Any suggestions are welcome please.

Thank you so very much for bearing with me lol
« Last Edit: February 05, 2014, 03:33:54 PM by Martin0121 » Logged
renewablejohn
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« Reply #1 on: January 28, 2014, 05:03:58 PM »

What make of biomass boiler is it.  Just quickly looking at your figures the feed temperature seems very low. What is the feed  temperature as it leaves the boiler and when it reaches the first distribution point. What sort of distance between boiler and first distribution point.
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Martin0121
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« Reply #2 on: January 28, 2014, 05:11:39 PM »

I dont know what make of actual boiler it is in the barn, i can take a look later when i go to check the level of wood chip.  the distance from the boiler to my house, which is furthest away, is about 100 meters max.  I do have data showing the in flow temp for the bungalow, (40m from the boiler) is about 81c, then our 3 houses in a row are about 78c, 75, 72. No idea what it is at the boiler either, i will try to find out.

Are the return temps supposed to be so low too?
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dhaslam
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« Reply #3 on: January 28, 2014, 05:12:39 PM »

One thing that may be causing the problem is the high  flow temperature combined with  radiator thermostats.     The water flow goes around the full circuit in the house and  into radiators that have the valves open.    When no heat is needed there will be a big heat loss just in the pipes  and also some radiators valves are not very good at  closing  fully. The low flow rates suggest that there isn't free flow through multiple radiators, normally a circulation pump will circulate over 1000 litres per hour.  Also the temperature drop of  30 degrees is a lot  which again  suggests  that  the system is just ticking over by sending a small amount of water through a lot of pipes.  It is better to have time/temperature control on  individual circuits which fully closes not needed circuits and  a main shut off valve when no heat is needed.     I suppose that  the same problem  may not arise with individual boilers because they would be use on a timer.  

Note that the heat needed to raise the temperature of a house involves heating quite a lot of  mass in the form of walls etc  but normally thermometers measure air temperature and the temperature of the house structure can lag behind.   A house can absorb heat while cooling if the walls and floors are still taking heat from the air with consequent output from the radiators.    

Biomass is not necessarily low cost and I wouldn't be surprised if the landlord also loses on  the transaction because there would be a lot of heat loss between the boiler and the individual houses.  
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Martin0121
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« Reply #4 on: January 28, 2014, 05:18:57 PM »

The Alpha2 pumps do allow us to set flow speeds, 3 on a constant pressure curve and 2 on a self variable curve, I currently have mine set on the lowest constant one in the hope that it would slow the flow to allow the exchange to transfer more heat to the water before it pushed it into the rads, i have the 1bed set on lowest variable, and the other 3 bed is on the highest constant.  i cant seam to find a difference in the end temps to be honest.
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Martin0121
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« Reply #5 on: January 28, 2014, 05:21:11 PM »

Also, re the high flow temp and TRVs, in my prior tests, i had everything set to max, and there was still no change in the time it took to heat the rads or rooms, it just used more kwph and thus cost more.
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Bodidly
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« Reply #6 on: January 28, 2014, 05:33:42 PM »

Sorry I can't help with ins and outs of your system but 5pence per kWh does not sound too bad and is less than oil according to this chart of prices.
http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,59188&_dad=portal&_schema=PORTAL
« Last Edit: January 28, 2014, 05:41:08 PM by Bodidly » Logged
Martin0121
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« Reply #7 on: January 28, 2014, 05:37:30 PM »

ty Bodidly. didnt know what other schemes might charge tenants.  but sounds fair enough, 5p pkwh is less than oil (oil is about 7.3p pkwh just now) but the system was far more efficient with oil by the sounds of it, it actually cost less to heat with the oil.  The price we pay for going green lol
« Last Edit: January 28, 2014, 05:39:59 PM by Martin0121 » Logged
brackwell
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« Reply #8 on: January 28, 2014, 05:46:34 PM »

How are you getting these kwh figs from?

In a high thermal mass property with plenty of draughts you are going to have real issues measuring heat.    You can quite quickly and cheaply raise the temp of air but this is just a transient situation.  When you turn the heat source off the walls etc will suck the heat out and draughts will make it happen double quick.  Therefore the running costs on a continuous basis can only be evaluated once the thermal mass of the building as been brought up to temp.  At this time of the year this will take days,depending on insulation and draughts.

Taking the eg of 249l/h at 76C in 46C out.  This equals i believe 15.9kwh.  This is not a lot when starting with a cold building and indeed in a exposed house in the highlands with large draughts this might only be just enough to maintain the status quo and therefore on non windy days the temps will rise and vice versa as the balance between heat loss and gain is established.

If you have big draughts on a windy day then if you switch the heating off the air temp will plummit but the temp of the thermal mass of the house will take much longer.  It is this interaction of heating cycles/draughts/thermal mass which makes it very difficult to reach conclusions.

Having a first stab at your questions then-

1) I cannot see how changing the heat source should make much difference to the efficiency ie heat transfer from the source to the rads.  Assume the pipe work and hence distribution losses are the same.
2) Yes for the reasons above
3)  Ditto
4)  Ditto
5)  I suppose this depends on the cost of oil v chips (hope they are dry)
6)  Similiar to the price of gas so perhaps fair
7)  Lots but lets both get on the same wavelength first.

One of the problems could well be that the system is just not big enough to cope.  I wonder if any heat loss calculations were done- i doubt it and therefore wonder how they came to fit this size of boiler.

Ken
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chris_n
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« Reply #9 on: January 28, 2014, 05:50:41 PM »

Are these temperatures across the boiler side of the heat exchanger? If so then the radiator side is only seeing a rise of 30degrees, i.e. the rdiators only get warm not hot.
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Jonah
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« Reply #10 on: January 28, 2014, 05:53:06 PM »

Is this 5 separate systems? (4houses plus one flow n return) or all separate f&r? Are they sealed systems or open vent? Do you have any rads without TRV? Is there a system bypass fitted? How/what controls the pump? Are they modern rads? Have you tried the pump on the auto adapt setting? Does the boiler feed a direct/indirect thermal store/tank type of thing?

When you're measuring the temp differential on the f&r is that to the heat exchanger? Personally I'd try and balance things up on the lock shields to lose more like 15*  (at each rad) it would be 20* on a gas boiler they'd have a better differential on the gas heat exchanger so pick up easier...  Are they massively under sized rads? 30* is a hell of a lot... But still depending on the efficiency of the heat exchanger you should still be able to get good heat from flow of 72* the rads won't be bouncing to touch but the rooms should get warm...
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Martin0121
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« Reply #11 on: January 28, 2014, 06:11:48 PM »

Jonah, each house has its own method of exchange and its own F & R. 
I dont know if they are sealed or open, ill check with the LL when he gets back.
In my house (the end 3 bed) there are no rads without a TRV, but the bathroom in the 1 bed doesn't have one.
From what i can tell the system has a automatic bypas (am only going from the crappy intstallation guide that was in a drawer).
The pump is controlled by simply being on or off from a Timer/control panel.
they are modern rads, ish, id say 5-10 years old.
I have tried my pump on both the high and low auto adapt and both resulted in even cooler rads, and higher KWH use.
I think from what i saw in the boiler room there is a giant thermal store, dont know the capacity but its about 10ft high 6ft diameter cylinder.

the F & R measurements come directly from the meter attached to the heat exchanges, the usage in kw comes from this also and works from the flow return pipe.

The rads look like they should be the right size in the 1 bed, one or two on our house look too small.

If this problem were just on one of the houses id get it, but its on all of them.
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Martin0121
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« Reply #12 on: January 28, 2014, 06:13:26 PM »

Chris_n,

All these readings are from the heat exchange and internal temp of the house.
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Martin0121
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« Reply #13 on: January 28, 2014, 06:16:05 PM »

Ty brackwell / Ken

The figures are coming directly from the meter attached to each heat exchange which give us the meter readings for billing as well as the operational readings at 1 minute intervals.

I realise that if the house walls etc are cold the system will have to fight to cope with the loss into the infrastructure, which is why i have given my house as an example as well, and even there, the heat and time it takes to bring the temp up in the rooms and the rads is huge and out of all of the houses mine is probably the best heated, downstairs at least, due to the high and fairly constant temperatures achieved by using the log burners.  there are no direct draughts in any of the houses but the walls are not insulated in any shape or form, and in the lofts there is a bare minimum of 100mm i think, so not very well insulated again, but the lofts are tiny as our upstairs are essentially the roof.

yes i find it hard to believe that the system is now worse than with oil as you are correct in saying all the pipe work and hence distribution losses are the same, but it is, by far.  I do wonder if this is also part of the problem, that the pipe work etc is the same as it was for the oil, if it is microbore ( i dont know as i would need to lift floor boards) or normal 15mm, could this effect the flow and heat exchange, either way round?
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Jonah
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« Reply #14 on: January 28, 2014, 06:30:14 PM »

Realistically even if micro bore or 15mm it wouldn't matter too much as any heat loss from pipe work in the house is heating the house anyway (to a certain extent) if all the pipes were buried in concrete floors or in 2ft thick stone walls it would be an issue.  Can you measure individual radiator f&r temps? That'll give you a better idea
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