Calculating fuel use to different zones in house - anyone good at maths?

[peterpumpkin]

Hi - we have a pellet boiler that heats three zones. I want to be able to work out what percentage of the fuel and maintenance costs to allocate to the different zones - reasonably accurately. I looked at heat meters but saw that they were expensive. I then thought of monitoring the pumps - if I knew how long each pump had been running for a period of time, then calculated the percentages, I could divide the fuel costs up in those percentages. I found some small digital meters that now monitor the electricity consumption in watts. NB - this should work as long as pumps aren't run with all the TRVs closed - ie not using much fuel; it's more likely that the TRVs in all zones will be set in a similar fashion.

My problem is that two of the zones use Grundfos Alpha2 L15-60 130 pumps and the other one uses a Grundfos Magna1 25-60 180 pump. I need to find out if these pumps, on average, will use a similar amount of power - ie whether or not the electricity consumption of each pump will be fairly indicative of the fuel consumed when calcuated as a percentage of the total amount of electricity consumed - or if I will need to tweak the figures to take into account the electricity consumption of the different pumps.

Cots will be shared by two users - one having the two Alpha2 pumps and the other having the Magna1. Hot water is less important because costs will be split 50/50 by agreement (but this pump is metered in the same way).

Any ideas? Thanks!

 

[albatross]

You are trying to make your life very hard!
Just simplify it by dividing by 3 or other estimation.
You seem to want the accuracy of heat meters without paying for them.
A compromise may be 'hours run' meters on the pumps.

 

[Roger Welton]

Unless all zones are identical, hrs run will mean nothing.

 

[Ermintrude]

Unless all zones are identical, hrs run will mean nothing.

Fit some expensive looking rubbish a few old pcbs and a USB stick, just blag it because any thing you do unless you have meters is a blag.

 

[Nostrum]

You can do it by calculating the heat loss of each zone then using historical data (degree days) to make an assumption of the annual usage per zone. By adding them together (or calculating as a whole house) you'll get an annual requirement for the entire building which you can compare with your fuel usage. For wood pellet your looking at approx 4.8kwh per kg of fuel used, so if you know your annual fuel usage you can charge for the percentage of fuel used per zone.

This will give you a ball park figure, but them you have the problem of people being in more than others etc

if you need accuracy you'll never get it without heat meters. Just using the pump as reference won't tell you what load is being applied to each zone.

 

[lame plumber]

so you do all the calcs and the bod in the other half just turns their room stats up to 28 and youll end up out of pocket, just divide by 3 for an easy figure and install some electronic thermometers in their side to check they arent being greedy

 

[peterpumpkin]

so you do all the calcs and the bod in the other half just turns their room stats up to 28 and youll end up out of pocket, just divide by 3 for an easy figure and install some electronic thermometers in their side to check they arent being greedy

Thanks for you replies, guys.

The zones are pretty much equal in size. So (let's say there are 3 zones) if, in a given period, zone 1 pump consumes 20kW, zone 2 pump consumes 60 kW and zone 3 pump consumes 30kW and the pellet consumption in that period is £1000, I'd allocate £200 to zone 1, £600 to zone 2 an 300 to zone 3. If the pumps were all the same size, wouldn't that be fairly accurate?

 

[Chalked]

Stop being so tight.
Your obviously the main user. So your also the main benefactor . Buy and install heat meters.
Job done.

 

[Nostrum]

Thanks for you replies, guys.

The zones are pretty much equal in size. So (let's say there are 3 zones) if, in a given period, zone 1 pump consumes 20kW, zone 2 pump consumes 60 kW and zone 3 pump consumes 30kW and the pellet consumption in that period is £1000, I'd allocate £200 to zone 1, £600 to zone 2 an 300 to zone 3. If the pumps were all the same size, wouldn't that be fairly accurate?

No.

using this method wouldn't work, be inaccurate and unfair.

 

[Ermintrude]

Sounds like op wants it that way and just wants belly tickled.

 

[happyflyer]

It cannot be done other than by fitting heat meters, the power consumed by the pumps is totally irrelevant, if it was relevant, no one would make heat meters, just split the cost, by area or whatever and come to some agreement or rip the system out and start all over again with two separate systems.

If you do find a way to do it accurately without fitting heat meters please tells us all and we can learn from it, it's good to learn even at 70, I will then patent it a make lots of lovely dosh!! Ermi don't know if a tickle will work either.

Peter, please give it up !!!

 

[zzzjim]

Do return temperatures give a clue ? but would need to graph them !

 

[happyflyer]

Do return temperatures give a clue ? but would need to graph them !

How does that work Jim?? Do you mean if he gives you a graph of the return temperatures from both circuits you could work
out the amount of heat being used in each circuit.

Be interested to see if you can make that work??

 

[Roger Welton]

How does that work Jim?? Do you mean if he gives you a graph of the return temperatures from both circuits you could work
out the amount of heat being used in each circuit.

Be interested to see if you can make that work??

This is how heat meters work, flow meter, and flow / return temps in then calculates heat dissipated from there.

 

[happyflyer]

Roger,

I know precisely how a heat meter works, just wondered where Jim got the idea from, we didn't give him chance and as you say, the flow meter measures
the flow rate and the flow and return sensors measure the difference and the integrator does the maths and you have Kws, even a small one say 22 mm would be about £600.

Thanks Roger

 

[Roger Welton]

If you know the flow rate of water and you know the temp drop then you can calculate the energy removed

Work Done = Temp Diff x Flow rate x Specific heat Capacity of Water (4.187)

 

[happyflyer]

I = m x cp x deltaT Just as you say Roger

 

[Nostrum]

Heat meter for the RHI, MID Class 2 with digital heat Integrator

 

[happyflyer]

Heat meter for the RHI, MID Class 2 with digital heat Integrator

Nice find, these are cheap too, have you used any yourself, they look good gear, this should do for the OP

 

[zzzjim]

It is a catch 22 , if you don't spend the money , or put a massive amount of time in (doing it manually) the answer will be full of assumptions and errors .

Thanks for explaining things Roger ( Instrumentation gets so expensive )

 

[happyflyer]

It is a catch 22 , if you don't spend the money , or put a massive amount of time in (doing it manually) the answer will be full of assumptions and errors .

Thanks for explaining things Roger ( Instrumentation gets so expensive )

Jim,

You can't do it manually you need to monitor the two temps and the flow rate on the fly, live.

Hand deep in pocket and spend