Heat meter readings for vigas biomass boiler

[grahamc]

We have an 80 kW vigas log boiler linked up to a 5000 litre akvaterm accumulator tank. The system heats a large farmhouse, workshop and office, and runs 24 / 7 in the winter months. It rarely shuts down, with the fan usually running at 100 %. We are dissapointed with the reading of the heat meter though, and feel that we should be clocking more kilowatts / day. We have spoken with the installer about this on many occasions, and in our last conversation with them we asked what kind of readings other customers of theirs might be generating. Below is an extract from their email, detailing what some of their customers are recording ;

 

 

a. 120 Kw (2 x 60Kw) boilers-2400 litre tank - 352Kw/day winter quarter. 287Kw/day autumn quarter.

 

Heats 4 x 'flats' within one large house and all hot water plus 60 Kw blower to dry timber in shed.

 

b. 40Kw boiler- 2500 litre tank. 92 Kw/day winter quarter. Heats two houses.

 

c. 100Kw boiler-5000 litre tank. 301 Kw/day winter quarter. 96 Kw/day summer quarter.

 

Heats farmhouse, workshop plus three cottages permanent lets.

 

d. 80Kw boiler - 5000 litre tank. 370 Kw day winter quarter.

 

Heats farmhouse plus 45Kw blower heating barn for classic car storage.

 

e. 40 Kw boiler-2000 litre tank. 75Kw/day winter quarter. 38Kw day autumn/summer quarter.

 

My question is, for those of you out there who run similar systems, ie manually fed log boiler and accumulator tank, do these readings sound about what you are achieving. These systems are running vigas boilers, but I imagine similar boilers will not be that much difference. Thanks for your time.

[ash_smith123]

Our 95kw attack runs at about 40/50kwh and 130kw eco Angus runs at 70kwh so whatever your KW is half it and that's about what you will get.

These figures from renewable energy companies are basically useless. You won't get anywhere near what they tell you.

[grahamc]

Thanks for the reply. I understand how you might never achieve what you think you might in peak performance, ie 80 kW in one hour from a 80 kW boiler, but the cumulative figures given are over a 24 hour period ie from the examples given above © 301 kW a day from a 100 kW boiler is averaging only 12.5 kW an hour, which seems incredibly poor. If an assumption is made that they are on 6p a kW, the return / day in the winter would be about £18, not a lot I feel, unless I am missing something.

[cornish wood burner]

Our 95kw attack runs at about 40/50kwh and 130kw eco Angus runs at 70kwh so whatever your KW is half it and that's about what you will get.

These figures from renewable energy companies are basically useless. You won't get anywhere near what they tell you.

Hi Graham

Are you saying your boiler is not giving it rated output or is inefficient?

You say the fan usually running at 100%, so presumably you keep it topped up with wood or could the fan be blowing your heat up the flue when the wood runs low.

Might be interesting to weigh a batch of wood and see what heat is recorded on your meter from it. That should tell you how efficient your boiler is.

Presumably your meter is very close to the boiler before your heat store so there shouldn't be much unrecorded heat

Sorry hit quote rather than reply

Edited February 10, 2017 by cornish wood burner

[cornish wood burner]

Thanks for the reply. I understand how you might never achieve what you think you might in peak performance, ie 80 kW in one hour from a 80 kW boiler, but the cumulative figures given are over a 24 hour period ie from the examples given above © 301 kW a day from a 100 kW boiler is averaging only 12.5 kW an hour, which seems incredibly poor. If an assumption is made that they are on 6p a kW, the return / day in the winter would be about £18, not a lot I feel, unless I am missing something.

 

Those figures depend on demand so small demand will result in a small reading on the meter.

[cornish wood burner]

Thanks for the reply. I understand how you might never achieve what you think you might in peak performance, ie 80 kW in one hour from a 80 kW boiler, but the cumulative figures given are over a 24 hour period ie from the examples given above © 301 kW a day from a 100 kW boiler is averaging only 12.5 kW an hour, which seems incredibly poor. If an assumption is made that they are on 6p a kW, the return / day in the winter would be about £18, not a lot I feel, unless I am missing something.

Depends on their demands so you can't really gain much info from those.

We run a 1 MW boiler through the summer but only expect about one MWh even on a cool day.

[Duncansimpson]

We heat 2 houses 100kw with 6000ltr accumulator and use around 250kw in summer and 450kw winter.

Year average is 380kw

[Duncansimpson]

We also burn around 45t of softwood every year which is much more than expected

[cornish wood burner]

We also burn around 45t of softwood every year which is much more than expected

 

Presumably you mean 380 KWh per day so assuming your boiler is 80% efficient and your wood is 20%MC then that is about right.

[grahamc]

Hi Cornish wood burner. Thanks for the input. The reason I mentioned that the fan is working hard all day is to get across that the burner is loaded many times a day, and is gasifying all the time. We have a large heat load, and if left without burning, the accumulator tank soon gets dragged down. We sell a lot of firewood ourselves, and the fuel we use is all the softwood and poor quality hardwood that I don't wish to sell. However, it is very dry, having been dried in poly tunnels beforehand, and is always below 20%. Because of what I burn, I accept that I am loading more often than burning hard wood, but will still expect more kW / day. Regarding siting of heat meter, the boiler room is about 75 m from the house. I actually have an 80 kW and a 100 kW sited together, both running into the same tank. The 100kw is currently rarely used, but was installed to make use of the tariffs when they were better. I hope to install a kiln in the near future using the 100kw for the heat source. Because the 2 boilers are on different tariffs, they each have there own meter which records there output into the tank, and the 2 demands on the tank, ie our house and the workshop / office, each have another meter, so we have reasonably good records of what heat comes from each boiler and where it goes. We do suffer heat loss from the heat main, but only a small amount, no more than you would expect. The low readings stem from the meter sited only a couple meters from the boiler, before it goes into the tank.