Calculating approximate cost of baseboard oil heat

Danlang

I have installed an hour meter on each of the 3 zone circulating pumps of my divided house . I am looking for an approximate calculation of gallons of fuel oil used per hour of circulating water in the baseboard. My furnace is an older (1990s) Liberty Slant Fin 151k BTU , L30PT. with a Beckett burner. I am guessing that the furnace is working at at least 80% efficiency, keeping the system temp at 150 deg. The label on the furnace states "Burner Capacity Light Oil at 1.25 gals/hr. I am wondering if this is the figure that I would use to calculate my hourly cost per gallon of fuel oil. If anyone can help me with this concept , I'd be greatly appreciative.

HVACNUT

What's the end game? What do you plan to do with these numbers? 
Are you trying to divvy up the rent? 

EBEBRATT-Ed

The burner capacity may be 1.25 gph but the actual burn rate would be the actual nozzle installed in the burner X the pressure setting of the burner's fuel pump (normally 100psi but can vary)

Once you know how much oil the burner uses /1 hour of run time, (your oil tech can tell you the oil pressure and nozzle size) you could then install an hour timer wired with the burner motor.

The circulator pumps will tell you nothing

Jamie Hall

To know what the burner is actually using, you have to clock the hours it runs and the gallons used. It will vary, depending on the actual nozzle fitted and the pressure it's running at. You may be running close to it's capacity -- but who's to say? Ask the man or woman who cleans, tests, and adjusts your burner. They will also give you the actual efficiency which it is running at.

STEVEusaPA

Another thing is with a zoned system especially, you’ll probably find that you’re frequently bouncing off the high limit. So in other words circulator(s) will be running even when the burner is off. And if there’s a low limit or circ hold off, the burner will run without any circs running.
Also are all 3 circulators identical? What happens if you switch out an old energy hog for something super efficient.
As far as the end game, my guess would be to take you wattage numbers, come up with a percentage of the whole. Then when you fill the tank you can apply these percentages to what you paid for the oil.
Keep in mind if your using this to get tenants to pay for fuel, by law, any measuring device used in any commerce, requires a weights and measures certification, otherwise you’d lose in court. That’s why you see those stickers on fuel pumps, cash registers, deli scales, even the giant yardstick by the register at Home Depot has one.

Danlang

Wow ! Great input and quick! Just the kind of help that I was looking for. Now I understand that the pressure and nozzle size are key in the calculation and I hadn't even considered the possibility that circulating pumps could be of considerably different efficiency. So now with all this info , I will take a step back to reconsider how best to account for each tennant's oil useage. Thanks folks!

STEVEusaPA

For more fun, each zone will have different flow rates and thus will use different amounts of Btu’s for the same runtime.

EdTheHeaterMan

You will be best to do actual calculations after the fact. Fill the tank with fuel, take meter readings that day.

The next time you fill the tank take the meter readings again. now do the math.

You will need to take into consideration how many feet of baseboard element is on each loop and multiply the feet of the heating element by the hours of operation. That will be a total usage for zone A. Do the same for zone B and zone C.

These total numbers will not have any specific definition as in BTUs or Hours of operation. They are just totals of time multiplied by the amount of element. So just call them Q or some other designation that has no specific meaning

Now add all three totals together. That is the Grand total heating usage per $ it cost to fill the tank.

Divide each zone total into the heating Grand total to get the percentage of the heating usage for each zone.

That will be the percentage of the $ for the fuel delivery each zone used. Double-check your calculation to see that the individual percentage of each zone adds up to 100% (or at least 99.?%)

If this method is acceptable to each user of the system, then you can make up an Excel spreadsheet to make the numbers go fast each delivery.

This is an imperfect oversimplified method because there are more factors involved. A pump on a longer loop will pump less GPM than a pump on a short loop. Also, there may be variations in the same pump with no other zones operating compared to all the zone pumps running. Another difference is a pump that operates on a cold start will log more time pumping colder water on startup, than a pump that operates after another zone shuts off and the boiler is already hot. You will need more measuring devices to determine actual BTU calculations. As I said the method I described is oversimplified, but if you can all agree that it all balances out over time, then the simple method is the easiest.

As @STEVEusaPA mentioned, if there is ever a legal discussion about this method, and your clock or meter is not approved by the local Weights and Measures authority. You may as well just pay for the fuel and stay out of court. You will lose.

Jamie Hall

And, as noted by @STEVEusaPA , this is NOT going to be a legally enforceable figure. To use it, I recommend that you create an explanation of how you propose to divvy up the cost and get each tenant to agree, in writing, that this is how it will be figured and this is how their bills will be established.

EdTheHeaterMan

You will also need to account for service failures. If one zone gets air locked, the circ pump will not stop operating. This will make the failed zone have a higher percentage because that zone had no heat. Now that would not be fair, Paying a larger amount while suffering without heat until the repairman came to purge the air from the loop. Pay more for less heat is not an acceptable outcome.

Are you sure you want to do this?

STEVEusaPA

@hot_rod posted some stuff about this type of metering, I think used in Europe.
Can’t remember if he posted it here or i saw it in Idronics.

The best solution is to break it out into three small properly sized individual systems, individually metered.

EdTheHeaterMan

@STEVEusaPA
I remember installing a European BTU meter for a hotel owner in Cape May about 25 years ago. He wanted to charge the retail store tenant on the first floor for the BTUs he used from a common Heating / Chiller cooling system I installed. I told him he needed to install two. One for the total of the building and the other for the tenant. You need a benchmark to compare the zone with. He was sure that he could do it with one.

I'm not sure he ever got it operational. He liked to tinker. I just cut in the well adaptors and the flow sensors. It looked operational every season I showed up for the changeover. Whether the rent was adjusted for the heating and cooling usage based on the meter, I'll never know.

Danlang

Those are all great and helpful discussions, Thanks. I was especially intrigued by the mention of an airlocked loop! Good point! I have taken all of your great input and decided to just use the meter readings as a very general idea of how much heat is being used in each zone. I am on premises to monitor any possibility of any service failures and problems. Fortunately my tenants are very agreeable to my motives, and willing to pay their fair share for the heat. Very helpful discussions and I am awed at all of your astute thoughts and ideas. Thanks.