Heat meter - Fun & games

FreeBear

Been thinking about fitting a heat meter for a while so that I can get an accurate picture of just how much energy is pumped in to the central heating system here. With hard data in front of me, it will be much easier to select a suitably rated heat pump when the time comes without any guess work.

Having looked at the price of heat meters available on the local market, I can't really justify £200-400 (or £75-150 on ebay) that one would cost. However, there appears to be any number on Aliexpress from around £20. If I can find one with an RS485 interface (or MBus at a push), it should do the job.

Would anyone with experience of these things care to comment ?

QrizB

I haven't ever purchased a heat meter from AliExpress.

Based on other stuff I have purchased, however, it's likely to more-or-less work. However you'll have no guarantee of accuracy or calibration, and it won't be MID-compliant.

If none of those things are important to you, you'll be saving £150. If they are important, you'll have wasted £20.

FreeBear

I've used Aliexpress for a variety of low cost electronic bits - Not had issues with ordering/delivery or quality.

Not concerned about a heat meter being MID compliant, as I am not billing anyone for consumption. And as long as it is accurate to within 5%, that should be close enough. Certainly more accurate than a finger in the air estimate that a heat pump installer might come up with.

michaels

Out of interest, how do they work.  Even measuring for example the difference in temp between the in and out pipes you would also need to measure the flow to understand the rate of heat transfer?

FreeBear

michaels said:

Out of interest, how do they work.  Even measuring for example the difference in temp between the in and out pipes you would also need to measure the flow to understand the rate of heat transfer?

They measure the water flow (usually with an ultrasonic transducer), along with the flow & return temperatures. From there, it is a relatively trivial calculation to work out how much energy has been dissipated by the radiators. The advantage of purchasing a ready made heat meter is primarily the fact that it has been (hopefully) calibrated and does all the math internally.

michaels

Would be interested if you posted a link to a cheap Chinese one - what do they 'talk to' google home or smartthings hub or their own app - hopefully without wires?

FreeBear

https://www.aliexpress.com/item/1005006347826157.html - This particular one (appears) to use RS485 (Modbus ?) for remote communication. Perfect for me, as I already use modbus to communicate with other sensors dotted around the house. M-Bus is the more common interface, either hard wired or wireless (usually 868MHz).

If you want to integrate with Google Home or smartthings, you'd need to add something like a small ESP32 to do the talking. But as I am using Home Assistant, I just need a simple wired interface.

FreeBear

Messaged the seller asking for a manual. They've read the note, and haven't responded.... Not that it matters, I've scored a Landi-Gyr T230 Ultraheat for about the same money, and now need to find an mbus interface so that I can plug it in to Home Assistant.

michaels

If you don't link up, do these only show 'instant' values or can you also see total heat transferred over a period on the display?

FreeBear

Depending on model, you should get a current energy reading, a running total, flow rates, and temperatures (flow & return). Some will store data for the previous month that can be accessed via the display.

Once I get this T230 plumbed in and wired up, I'll post some of the data and maybe a graph. But with summer on the way, I don't anticipate running the heating until next winter.

michaels

FreeBear said:

Depending on model, you should get a current energy reading, a running total, flow rates, and temperatures (flow & return). Some will store data for the previous month that can be accessed via the display.

Once I get this T230 plumbed in and wired up, I'll post some of the data and maybe a graph. But with summer on the way, I don't anticipate running the heating until next winter.

Saw one just sold on ebay for 36.99 whereas all the ones for sale were closer to 100 - someone got a bargain....