Efficient gas boiler with real-time data (opens in new tab)

(emoncms.org)

47 pointspandora-health1y ago43 comments

I would like to share with you the real time performance of my condensing gas boiler, managed by SAT and OpenTherm.

Many gas boilers are oversized which means it's more difficult to run them efficiently. Also, many gas boilers have capability to run more efficiently but are not configured to.

This particular boiler does not seem to respect the MM=0 command (despite OpenTherm's such specification requirement) which is not uncommon. SAT sends the MM=0 command for the boiler to work at its minimum capacity. CS= minimum_setpoint and then PWM controls the ON/OFF times of the boiler. However, I have a workaround which ensures that most of the time, the boiler is indeed working at its minimum modulation, unless the target flow (heating curve + PID) demand is high [higher than current flow temperature] during warm up.

The boiler supplies heat to the central heating and domestic hot water tank, but not at the same time. The hot water tank capacity is 255 litres. When DHW call is made, boiler ignores OpenTherm instructions and runs at 80 C degrees. There are three zone valves in the house: Hot Water, Upstairs and Downstairs (not talking about TRVs here). When DHW call is made, Hot Water valve opens, and Upstairs & Downstairs close; then if CH call is made, Hot Water valve closes and the other two open.

The hot water system is also fitted with "Waste Water Heat Recovery System". In essence, the heat energy extracted from showers and baths is used to preheat cold water that is then sent to the hot water tank. The extraction recovers about 60% of heat normally lost. You can watch examples of how it works here - https://www.youtube.com/watch?v=G-jKlCoRvEM

SAT project - the brain behind the efficiency https://github.com/Alexwijn/SAT

OpenEnergyMonitor - for making possible to share real time boiler data https://community.openenergymonitor.org/t/my-gas-boiler-data...

Any questions, let me know :)

43 comments

blitzar1y ago

> The hot water system is also fitted with "Waste Water Heat Recovery System"

I really want one of these - the >40C water going down my drain being replaced with <20C water into my hot water tank keeps me up at night (figuratively). Such an easy win to exchange some of he heat out. It is on my shopping list for the next house / next renovation.

You should add dhw water temperature sensors to the mix too.

alliao1y ago

I've stopped worrying about it, I now use the heat with a packet of bio-enzyme to help dissolve any random bits of lard blocking up the waste drains, this is one of those unintended consequences scenario. I recall reading about California sewage got clogged up when enough people bought low flush toilets but the bigger street sewage pipes were never designed with so little flow.

NoMoreNicksLeft1y ago

Can substantial heat be recaptured? The sink drain's often pretty far away from the hot water heater in most homes. There might even be multiple faucets (not to mention shower/tub drains) in the mix. Seems less than feasible, but my intuition's often shit at figuring this stuff.

blitzar1y ago

You can preheat the cold flow into the shower so it is just local within the bathroom. Your hot water tap flows at the customary ~55C and the cold feed to your shower gets a boost to 25C or something.

Or you could send all the waste heat to a big sump and extract it with a heat pump (dont think that actually exists though - or would be some form of ground source heat) - at extreme temperatures would be worth it.

1 more reply

rainbowzootsuit1y ago

If you recover heat to the cold supply then you need less hot supply to get to the same outlet temperature. If you have an updated fixture with a thermostatic mixing valve then I think this would track pretty much seamlessly, but I've not ever had the opportunity to use a shower equipped this way.

btbuildem1y ago

Something as common as automotive coolant/"antifreeze" could efficiently travel via thin lines alongside regular plumbing.

I think a big part of the challenge would be in having multiple heat exchangers. Perhaps (if plumbing codes allowed) a plain p-trap could be swapped out for an exchanger unit that also serves as a sewer gas stop.

I don't know anything about thermodynamics; how long would it take to transfer a reasonable amount of energy from waste water into the coolant?

Another issue again, running all these coolant lines back to a central water heater w/another exchanger. It does all sound pretty complicated and expensive.