Interested in heat metering for multifamily building
I'm part of the board for a 20-unit residential condo building with a shared hydronic heating system, and we're interested in improving the fairness of how we split the gas bill by measuring each unit's heat use. I'm doing some background research to learn about potential methods and costs, so I'm interested in your thoughts!
System overview: Built in approximately 2000, one conventional gas boiler, one single-speed circulator pump, two loops. Supply temperature is 140F. Each unit is its own zone and has a little nook that provides access to the zone valve for maintenance/replacement. Units have total lengths of baseboard pipe between 20-35 feet. Most units have Honeywell Chronotherm III thermostats. This is in California, rarely gets colder than 40F outside.
What I've gathered so far, including from articles like this one and this one, with a few questions:
- In Europe, there are off-the-shelf heat allocator systems.
- Are these available in the US?
- Best practice would be to install a flow meter, supply temp sensor, and return temp sensor for each unit, then calculate the results.
- Professional, highly-accurate equipment wouldn't be in budget for our small building. We're just looking for something better than prorating by unit size. What are low-budget options, even if not as accurate? For example, I saw some clamp-on ultrasonic flow meters for $200-300 each (TUF-2000M series), although I don't know if they're appropriate to our needs. Also curious what kind of professional we'd want to hire to scope and install that sort of thing.
- The lowest-cost method might be to set up digital hour meters to measure how long each zone valve is open, if owners would accept the approximation (since each unit has a slightly different supply temp, different pipe lengths, etc). They might be up for it if installation is cheap and monitoring is easy.
- Interested in whether people have any particular suggestions for hour meters that could suit this purpose, including ones that could transmit data via wifi.
Thanks for any help!
Comments
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some additional info here. We did get an E3137 standard developed a few years back. So the btu meters listed to that standard should be accepted by your AHJ for metering and billing.
Check with the local and state interpretation some areas frown on owner billing if you are not a PSU, Public service utility
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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I would say the fairest approximation would be runtime times length of baseboard.
If you can avoid it, I wouldn't do Wifi. With 20 connections there's a lot that can go wrong. Typically the zone valves will have a wire that goes back to the circulator to turn the circulator on. If those wires all go all the way back you could measure on/off there.
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I believe the local regulations focus on landlord-imposed submetering of tenants, rather than condo owners submetering themselves, but it's a good reminder to make sure before we actually do anything!
Curious about equipment and costs for lower-end BTU metering options. I saw that Caleffi article and this post from Dwyer.
@DCContrarian Interesting, our circulator runs continuously throughout the heating season, and I don't think there are wires from the zone valves back to the circulator. Here's a photo of a maintenance nook - the zone valve seems to be wired to a little transformer and to the thermostat.
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What you are looking for is a heat meter ie:
These provide BTU/kWh by measuring flow and supply and return water temperature. Some units have pulse output which you can connect to a central monitor. I've used these for water metering before, should also work for pulse heat meter:
I think overall, the suggestion of monitoring zone valve on-time is close enough and less invasive install.
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looks like a balancing valve by the zone valve. So all units may have been balanced at one point. valve time open alone may not be enough info, with different flow rates in different units.
An accurate btu meters needs to sample every few seconds as the load is an ever moving target.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
How much money are we talking about? What is the average gas bill?
Since the baseboards range from 20 to 35 feet per unit, I'd assume they're roughly sized according to heating load so the biggest is 1.75 times the smallest. If the total bill is $400 and you're splitting it 20 ways, it might be $20 per unit now and range from $15 to $26 after metering. That hardly seems worth worrying about.
On the other hand if the bill is $4000 it might be worthwhile. Although even $50 per month may not be worth it.
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Just a thought but if some units have more outside walls than others they will be using more heat because they will have a higher heat loss. The heat from those units supplements the more "inside" units, If those units were not there or unheated the other units energy usage would go up, so at least some of that heat is a bit shared. While you can certainly meter how much energy goes to each unit I am not convinced it is exactly "fair" it's hard to get it truly fair imo, shared heating system feels like it ought to be a shared bill split evenly, everyone is using it.
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I think the problem with heat allocators is that there is a radio frequency conflict preventing simple importation of European devices to the American market and the American market itself is too small to justify the modifications necessary.
In Europe, HVAC products generally use the 868 MHz Band - in the US we use the 915 MHz band for the same purpose. Since these are simple, non-adjustable transmitters, it isn't possible to "retune" them easily (to avoid FCC/similar EU issues).
This is why all those European Smart Radiator Valve systems (Tado, Eve, Netatmo, Bosch) don't sell their products in the US and why Honeywell sells the HR92 in Europe (which can be synched via radio) and only the HR90 in the US.
You just won't find the same thing in the US or you'd have to pay a fortune in redesign fees.
That said, I find it hard to believe the North American market boiler market isn't big enough to run a production line that swaps 868 MHz transmitters for 915 MHz but otherwise operates the same.
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much of it is in the eye of the renters. They often feel they pay for their neighbors wasting heat or dhw in unmetered units.
A unit with the thermostat cranked up and the window open for a cool bedroom sleeping experience , for example should the renters split the cost?
The satelite boxes we build for flats in Europe meter cold water, hot water and heat. Some have card scanners so you pay as you go.Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
There's some American products listed in this thread:
That said, I've worked with some of these brands - you'll be spending $100,000+ to implement these kinds of systems in a 20-unit building. I suspect it isn't worth it and you should just divvy up the heating by SF and end up in a tragedy of the commons problem from those who keep their place at 80 degrees.
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I think you are heading down a road filled with pain and headache. Just split it evenly.
Here are the other inequities that will still remain even after you spend tens of thousands on such a system:
- Lower floors are paying for heating the floors above them.
- Neighbors who prefer it (or can stand it) cooler will be sucking free heat from their warmer neighbors. That's just physics.
- Units on the top floor although getting heat from below, will be losing some out the top, who will pay for that?
- Units on the corners will have more exterior walls and windows, they will have to pay for more heat (that might be considered the cost of having a nicer location).
- There will no doubt be billing errors due to temporary failures of the metering system. This will foment anger and possibly lawsuits (as might many of the earlier points)
- The additional cost and hassle of the maintenance and reporting of this system will be substantial.
- If you bill based on time run on the baseboard, does every unit have the same length of baseboard? Are they getting the same heat for the same runtime? The variables and intricacies of this are mind-boggling.
In this country people have a major problem if the other guy isn't paying "their fair share" or if heaven forbid something that I paid for might actually help another fellow human being. It's a problem. Come on, you live in the People's Republic of California (I say this with fondness, not vitriol) and it only gets down to 40 degrees. Surely these neighbors can enjoy what they have without worrying about a tiny fraction of their tiny heat bill.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el
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Thank you all, lots of good things to think about and research further! Appreciate both the practical and technical info, including @KarlW's details about why European heat allocator products aren't available here.
@hot_rod Yes, there's a little balancing valve by the zone valve! Hadn't noticed that before, thank you.
A bit more context:
- Highest gas bill last season was $2600 for 33 days (average of 28.6 therms per day).
- All units are on the same level (no units above or below each other).
- Units range from about 700 sq ft to 1400 sq ft.
If we can't come up with a low-cost and reasonably fair way to divide the bills by usage, we'll stick with the current process of prorating by unit size. That's fine.
Even if we don't change billing, I'd still be interested in a low-cost way to measure and report runtime, to help owners understand their heat usage over time. Some owners want to improve their conservation of fossil fuels, and seeing some charts can help people figure out whether it made a difference to fix their window seals or re-program their thermostat.
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Since each unit has its own zone valve I don't see the point of the balancing valves.
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Just for monitoring you could put an hour meter on each zone valve.
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@DCContrarian Yes! Interested in suggestions for products that could work in this context. The zone valves are Honeywell V8043F1093, and a friend noted that consumer-grade "smart home" gear is not designed to deal with things like 24V AC at low current. They suggested looking into putting a Shelly Plus 1PM UL on the input side of the transformer to track whether the valve is open vs closed.
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Doesn't it always come down to how much $$ to spend to get what info.
How many of the unit occupants would actual collect data and give it to who? What would an hour run meter mean to a tenant? Other than lowering their thermostat would reduce the run time. I'd guess most people figure that out just as they do gas mileage.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
My recommendation would be to get something like this to convert the 24VAC signal from the thermostat to 12VDC:
Then get a simple mechanical DC hour meter like this:
You'd have to enter the units to read them.
I'd think there's be affordable Wifi hour meters but I haven't found them in a quick search.
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As Bob mentioned you may very well run afoul of utility regulations.
A simpler method to do this would be to create an overhead gravity hot water system using a circulator controlled by a float to feed the open to air expansion tank on the top floor that would store the hot water.
In doing this the hot water created by the boiler drops to all the baseboards at once and then to the boiler where it is reheated and pushed to the open to air expansion tank and the hot water sinks to the baseboard.
You would eliminate a lot of electronics and trade that for simplicity and you have all the tenants get heat at once and they can control it by using a trv they would pay for or by simply stuffing towels in the baseboard to slow down the heat.
The fuel cost would simply be divided between the 20 tenants as a whole every month.
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