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Author Topic: Help and advice needed Please, Biomass DH costing a fortune to run  (Read 30569 times)
Martin0121
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« Reply #135 on: February 06, 2014, 05:37:12 PM »

Mostie, the houses and the boiler are isolated from each other and have different pressures and flows but we only ever see 72 to 77 deg flow.  they do need 78 according to the sheet i was just given by the installers and they need a flow rate of 0.3l/s that works out at 1080l/h we are only getting 310l/h.
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Martin0121
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« Reply #136 on: February 06, 2014, 05:45:46 PM »

OK all UPDATE:

Landlord is back so can answer questions and change stuff now, so let me know.

yesterday I did check clean and lube all my TRVs, none of them stuck and none damaged.

Ran the heating as normal on the settings I had always ran it on, no change (jsut to give a base line), then i ran on all trvs on 2, no change in anything apart from the rads didn't even get as warm as they did on frost protect, flow rate, F & R temps, kWh usage all the same, then ran TRVs on Max, same result lower rad temps no change in anything else.

still getting cavitation on my pressure gauge.

also today, the extra boost of random return flow temps we got from last Thursday onwards, had stopped,  the  return temps are back to about 42 even after 2 hrs, DeltaT of 30 again, where as from Thursday until today we got R temps of up to 68 and deltaTs of upto 7deg, the rads were nice and hot back then even after only 45-60min.  But not now :-( nothing in the boiler or houses has changed from what we can tell.
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knighty
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« Reply #137 on: February 06, 2014, 07:07:35 PM »

there's a lot of info in this thread and it's hard to keep up with it all


can you tell us the flow and return temperatures from the boiler side of the heat exchangers

and the flow and return from your central heating side



if you're hardly getting any heat, but also only paying 5p/kwh and it's costing a fortune to run it doesn't really add up
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Martin0121
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« Reply #138 on: February 06, 2014, 07:24:17 PM »

No Probs
Boiler side: Flow temp 78.8c return 67.4c
ours 72.4c return 46.3c (these are after 2hrs use today)

Also today i got a data sheet from the commissioning team showing some of their temps and readings, none of which are any where close to the actual readings we are getting.  i have attached it and cottage 4 is my house.

* Commissioning Notes.xls (18.5 KB - downloaded 123 times.)
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knighty
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« Reply #139 on: February 06, 2014, 11:12:04 PM »

according to those commissioning notes

the flow rate coming out of the boiler house is (supposed to be) 1.55litres/second (93litres/min)
93litres/min isn't  enough to heat 7 houses imo
the flow rate to your house is (supposed to be) 0.3litres/sec - 18litres/min.... which will struggle to heat your house unless your heating is on 24/7

but... I guess those numbers have to be taken with a pinch of salt...


Quote
Boiler side: Flow temp 78.8c return 67.4c
ours 72.4c return 46.3c (these are after 2hrs use today)

I know it was posted earlier, but did you try turning your pump speed up ?  that should help you heat up a lot quicker...

(unless... the heat exchanger unit is limiting the flow to keep the boiler return temperature up high enough... can you see anything that could be doing this?)



it doesn't really matter if your heating system is slow to heat up... the problem is that it's costing you so much to run it... so I think you really need to check the metering system first...
(if it's slow to heat up, then you can't be using that much heat, so it should be cheap to run?)
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Countrypaul
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« Reply #140 on: February 06, 2014, 11:58:52 PM »

1.55L/s with a 10C change in temerpature I make about 65kW - (1.55 L/s * 10C * 4200 J/LC) so about 9kW/house assuming full time operation.

0.3 L/s with a 25C temp difference is about 31kW so that looks very suspicious to me, as unless you have an uninsulated tin roof, 31kW in a cottage should keep it quite toasty.

Either the pump is not passing 0.3L/s which could well be the case if it is cavitating, or the me metering is out, or both imho.
« Last Edit: February 07, 2014, 12:00:32 AM by Countrypaul » Logged
brackwell
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« Reply #141 on: February 07, 2014, 09:18:33 AM »

  You have a pump that is probably cavitating, a small flow rate which does not change, TRVs having no effect. This must be blocked flow must it not? So putting thoughts on the table.

1) TRVs the wrong way round.
2) A isolation valve perhaps either side of the pump is partially closed.

Where exactly are the gauges/readings being taken?  All your house side of the pump?

Ken
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derekmt
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« Reply #142 on: February 07, 2014, 11:38:12 AM »

  You have a pump that is probably cavitating, a small flow rate which does not change, TRVs having no effect. This must be blocked flow must it not? So putting thoughts on the table.

1) TRVs the wrong way round.
2) A isolation valve perhaps either side of the pump is partially closed.

Where exactly are the gauges/readings being taken?  All your house side of the pump?

Ken
Add
3) header tank or expansion vessel on wrong side of pump
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knighty
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« Reply #143 on: February 07, 2014, 07:51:25 PM »

the cavitating pump shouldn't make any different to his metered heat use because the cavitating pump is on his side of the central heating, not the boiler room side ?

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regen
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« Reply #144 on: February 07, 2014, 08:18:04 PM »

This is a really interesting thread  but has anybody really looked at the front end! What is the MC of the chip being used? Is the MC variable? How much is being burned per hour or day and how many KWH is this producing approximately.  Is the boiler burning continuously  or are there long periods when it is idle? What is the approximate expected usage per hour or day for all the houses combined and how does this stack up against the fuel input per hour or day?

Regen
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3.92w freestanding PV with sb3300 +Imersun
21kw Stratford T70 woodburner
 300litre thermalstore with 3kw and 1kw immersions
 Wall star 25kw oil boiler
  Spring water supply with uv and ro membrane
 Sheep, poly tunnel and approx 80 sq m of raised veg beds.
Mostie
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« Reply #145 on: February 07, 2014, 10:53:40 PM »

i like when other peeps do the maths regarding flow rates and stuff....  crack

Martin a thought struck me when you said the flow and return temps were ok for a bit..... so back to the Grundfos pumps in the boilerhouse, did they do a duty changeover? Which pump was running? Has some idiot set up one pump and forgotten the other so the speeds are different? I've seen it happen, or has the phantom button presser been at work  whistlie
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2x Solis PV = 1.875 kW, Mitsubishi inverter heat pump. Yorkshire Boiler Stove.
brackwell
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« Reply #146 on: February 08, 2014, 09:22:45 AM »

My thought for today is air is in the system.  The loop pipe (buffer to houses) rises, therefore any air in the system will sit close to Martins house.  Is there a means of bleeding the system at this end? It is necessary to bleed the system including the rads many times before getting rid.  Of course if the loop does have air and this is removed then need to be sure this is replaced.  The air will come because it is dissolved in fresh water and comes out when the water is heated.  Some one said on here years ago about this and i seem to remember talking about 6% is air?

I have found air to be a problem when fitting my solar thermal and when replacing the pump on the DHW tank.  Just had to keep bleeding.

Ken
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Martin0121
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« Reply #147 on: February 08, 2014, 10:54:53 AM »

this is just a quicky, am visiting family just now.   

the pump in my house is set on max the one in the boiler room is set on 50%. we upt that from 40% and it made no difference.  we can put it up higher after we have had a meeting with the installer later this week. I can stop the cavitation on my pump by putting my setting to 2. but then we get even less flow and lower temps.

their flow readings work out to be that our house should be having a flow rate of 1080 litres per hour and we dont get close to that, we only see 310 to 360 max.

the return temp we get of 42 ish is far too too low.

bear in mind that this is not just isolated to my house the issues are accross all the houses in my section so points,  in my head, to the boiler or pipe system
. or multiple cock ups on the exchangers.
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Martin0121
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« Reply #148 on: February 08, 2014, 12:12:22 PM »

added note. the landlord has told me that he knows the 133kw boiler is undersized for all 7 houses all using heat at the same time. but so far they havent needed to all be on at thr same time and the oil boiler is there and designed to kick in for the short fall.
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Mostie
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« Reply #149 on: February 08, 2014, 02:39:35 PM »

sorry, I may have missed a bit of this thread, just found all the pictures  facepalm
I think this is your heat exchanger

http://www.termix.biz/Admin/Public/DWSDownload.aspx?File=Files%2fFiler%2fProduct+sheets+-+GB%2f05+Substations+Indirect+Heating%2fVLHEM112_Termix_VVX-I-with_compl_insulation-1207.pdf
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2x Solis PV = 1.875 kW, Mitsubishi inverter heat pump. Yorkshire Boiler Stove.
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