zoning and balancing with TRVs

roundrightfarm

greetings everyone,
I'm designing a panel radiator system. It will have a mod-con boiler w/buffer tank and will use a manifold distribution system. I'm hoping to have a single, pressure sensitive circulator on the manifold side of the buffer tank. It is heating a 4 level building with a finished basement, 2 main floors, and a finished attic.

I was hoping to do most of the zoning with TRVs, but I'm wondering if they might be limiting for the desired amount of control. The attic will not be used year round, and I'd like to be able to set it back to 42F when not in use. Is this possible to get this wide a temperature swing between the atttic and the rest of the house with a TRV or will I need a thermostatic valve actuator for the attic radiators? If using TRVs instead of a centralized thermostat for the rest of the house, will I be able to take the whole house down to 42F when we go on vacation? Or, can this be realized by having a vacation setting of a lower buffer tank temperature?

Also have a question about balancing with TRVs. Is the best practice to leave the TRVs fully open and then balance using the lockshield valve? Doing it this way, will the system take itself more out of balance as more TRVs shut down?

thanks

hot_rod

TRVs generally have a vacation mode, as well as a freeze protection setting.

Keep in mind, unless you have good insulation values ceiling, walls, floors, between the various rooms it will be tough to have wide temperature differences in rooms under the same roof.

SWEI

You might consider a conventional electric zone valve for the attic.

Here is how we balance with ODR and TRV's: Leave the lockshield valves all the way open. Crank all the TRV's up to maximum. Now adjust the boiler's ODR parameters (this can take a week or three, or even a whole season) until the coolest room is comfortable and the indoor temps are consistent regardless of the outdoor temp. If all the other rooms are close in temperature you can skip the next step, which is to dial down the lockshield valves on any rooms that are overheated. Now go back to the boiler and raise both ends of the reset curve several degrees -- until the house is is 3-5°F hotter than you will normally want it (perhaps even more if you have aging family members or guests.) Now adjust the TRV's to get the temp you want in each room. This way you get comfort in every room with the TRV operating somewhere near the middle of its range.

roundrightfarm

Thanks for the advice.

Since the attic radiators will have the longest pipe lengths, will this mean that they will be the most open of all the balancing valves? Given the height of the attic relative the basement where the boiler is, will I have to add any special design considerations, or is pipe length the only factor to consider here?

SWEI

As usual, it depends -- in this case, on the piping layout. There are several options for that space depending on your outdoor temp range and building construction/layout. You don't want those pipes to freeze, and there are several approaches to preventing that.