Improving hydronic performance with TRV?

Hitchum

Hey all,

I’m looking for some advice on improving the performance of a poorly performing hydronic heating system.

The system is installed in a two story building, with the boiler located on the upper floor. Heat is distributed to both floors via baseboard convectors piped in a series circuit. The circuit on the lower floor has been tee-d off from the upstairs circuit. I've attached a diagram to illustrate the layout.

Hydronic System.png

The lower floor is difficult to keep warm in winter for a couple of reasons (1) the upstairs circuit receives the lions share of circulation since it has a lower resistance (2) the only thermostat is located upstairs, and (3) the lower floor has higher heat losses.

Ideally the system would be converted to a zoned system, but practically speaking this is difficult to pull off, as the tees for the lower circuit are located above finished ceiling 20’ away from the boiler.

As an alternative I was considering placing a second thermostat downstairs, and using an inline TRV on the upper circuit to throttle / balance flow. I have sketched these additions in the diagram in red.

Would appreciate anyones thoughts on this route or other suggestions!

Niall

DCContrarian

The best comfort would come from using zone valves. They don't have to be at the tee, they can be at any point on the loop. Is there room inside the case of the baseboard? Then it's just a matter of finding a route for the thermostat wiring from the thermostats to the zone valves and back to the circulator.

A TRV would work. But the upper zone could only get heat when the lower zone is getting it. The issue would be when the upper zone needs heat and the lower zone doesn't. Your choice would be either to have the upper zone wait until the lower zone calls for heat, or deliver heat to the lower zone even though it doesn't need it. Also, TRV's don't give as consistent comfort as zones, because you can't put the sensor very far away from the radiator. With zone valves you can put the thermostat on the other side of the room and it more accurately reflects room temperature.

Hitchum

Thanks @DCContrarian

Great points. I did consider installing zone valves further along in the circuit. Unfortunately there's no great location … they would end up either quite far from the boiler (hard to route the wiring), or in the finished ceiling (maintenance headaches). I'm assuming a zone valve should be easily accessible for service or replacement every couple years?

If installing a TRV I would have a stat on each floor, so either could call for heat. The drawback, as you point out, is that regardless of which stat calls for heat, the upper floor needs to heat up first so that the TRV will choke down and provide adequate flow to the lower loop. That might actually be a workable arrangement, as the upper floor is where the living spaces are and should have priority. It would be rare to want to heat the lower floor and not the upper.

Another thing I'm battling with here is that all the piping is 3/4" copper. So there is a bottleneck on heat transfer in the system (40K BTU at 20 degree delta-T according to the rules of thumb I've seen). This seems to force my hand into running additional pipework … meaning I'm back to opening the ceiling or lifting floorboards again. :-/

EBEBRATT-Ed

@hitchum.

You are correct that 40-45,000 is the limit on 3/4 baseboard or about 70' of fin tube max per zone. I hope the supply and return to the boiler ar at least 1" minimum.

Sometimes it's best to go back to the basics to confirm what you have.

do a heat loss

size the baseboard to the heat loss

size the piping and pump

I am not trying to reinvent the wheel but it's easy to miss a problem or mistake 1 problem for another.

Zone valves are the better fix

hot_rod

TRVs would be ideal, they are a non electric proportional, temperature control valve.

Two TRVs with a delta P circulator. A flow switch or induction relay on the pump.

I think some circs now have an end switch contact.

TRV calls for heat, delta P circ revs up, boiler is enabled by one of 3 options mentioned.