Flow Settings for Home Run Piped Emiiters with TRV

tropostudio

Quick summary of my hydronic heating system, commisioned in 2018:

59 KBTU/h heat loading at coldest design day. 80 KBTU/H mod con, fire-tube boiler. Calculations are for 30F Delta T and 140F supply/110F return for -10F design day.

A single Grundfos Alpha Circulator (no P/S pump). 15 home run emitter loops - 5 per floor, distributed via Uponor SS manifolds. 12 loops use 3/8" PEX, 3 loops loops use 1/2" PEX.

I've calculated a 3.9 gpm system flow; 0.70 ft. head loss across combined parallel loops w/ emitters; and 2.06 ft. head loss across largest single loop with emitters. Every panel has an Oventrop TRV.

Here is how I have been setting loop flows: First, I set each TRV at '5', which should have them 'wide open' while I set flows. I run the Alpha at it's lowest constant pressure mode setting, which ostenibly maintains 6 ft. head. This is well above the calculated drop for my total system, but is as low as the Alpha will go I then adjust each loop's flow valve to match my calcs. Calculated loop flows range from 0.1 (a bathroom) to 0.5 gpm (living room).

I still have a nagging feeling I missed something in how I balanced it. The flow and head loss calcs include an equivalent length allownace for a 'valve' at each loop, but how do you actually account for the fact that each loop has a flow valve and a TRV - with the pressure drop across the TRV varying over time? Should I be following a different procedure

FWIW, my TRV's are set to '3' (68F) and I leave them alone. The house temps stays at a consistent 68F all Winter. The house is quite tight and well-insulated. The system generally just cruises along, with very little ramping up and down (except after the indirect DHW steals a call for heat).

Jamie Hall

Don't overthink it. If your TRVs are controlling the space temperatures the way you want them… what's not to like?

hot_rod

the TRVs and the Alpha should do the balance for you.

TRVs are proportional valves, not open / close like zone valves.

If the Alpha is getting the job done at its lowest setting, what’s not to like?