piping and boiler reset questions

heretic

That's a lot of questions. Sounds like "paralysis by analysis" may be setting in...

Specifically regarding the Munchkin:
If you use the Vision1 controls, the boiler will modulate in response to direct input from the OR sensor, and produce a variable supply temp when in space heating mode. There is no water temp sensor to place in this scenario.

Their install diagrams show the DHW and space heating primary as parallel loops (priority, so they never both run), then secondary loops for each space heating zone.

Jamie_5

piping and boiler reset questions

Background facts: I am a home owner in Brooklyn conducting a long-term renovation of a rowhouse while I, my wife, and her two children live in it. We are doing the work ourselves and making mistakes as we go. Some will never be fixed, but even the mistakes are better than what we started with.

We figured out that our boiler is massively oversized at 200,000 BTU. (Using Siegenthaler’s Hydronic Design Studio, we calculate that the house should lose 30,000 BTUH when we finish the insulation and door and window replacement.) Unfortunately, we did not learn enough about different piping methods until we had already piped in two rooms irretrievably. (The pipes are now covered by a base layer of drywall, with a layer of soundboard and another layer of drywall glued on top and a vapor barrier and fiberglass insulation between the exterior brick wall and the studs which mount the initial layer of drywall. All for sound deadening; we both play drums. Anyway, those walls and celing are not coming down, so the piping will stay as it is.) Those two rooms are a small studio and the kitchen. They are piped as the next to last and last circuits in a direct return system and have cast iron baseboard radiators for heat emitters. The lower level room---the studio---has a TRV on the radiator.

The rest of the house has old, battered, fin tube convectors piped in a modified direct return system that is essentially what we inherited with the house. We want to put radiant baseboard in the rest of the basement and main floor and panel radiators with TRVs in the bedrooms on the top floor. We also want to use constant circulation with outdoor reset, replace the old water heater with an indirect-fired one, and use a condensing boiler. (Among other things, we don’t trust the existing masonry chimney and there is no place to vent safely through a sidewall. So we would like to run CPVC or PVC intake and exhaust through the existing chimney. We also assume that a condensing boiler would make piping for lower reset temperatures easier and that a condensing boiler would operate more efficiently at those lower temperatures.)

So I have two basic questions. First, is there any reason we can’t pipe the rest of the heating system as a simple series loop with the studio and kitchen coming as the second and third heat emitters in the system and pipe something like Buderus panel radiators into it using their diverting valves (which I assume operate essentially like Monoflo tees)? In other words, is there any reason the circuit shouldn’t go (1) radiant baseboard, (2 and 3) cast iron baseboard for studio and kitchen, in parallel, (4, 5, and 6) panel radiators with diverter valves and TRVs, (7) radiant baseboard, (8), final panel radiator with diverter valve and TRV?

Second, if we choose the Munchkin T50 as our boiler and pipe it so that it is a secondary circuit to a primary circuit which is itself two parallel circuits (the series heating loop and the DHW loop), each with its own circulator and the DHW loop on priority, would placing the reset supply sensor on the supply side of the heating loop and wiring the reset controller and a thermostat in series to the thermostat connections of the boiler work? My main concern is that because the Munchkin uses supply and return sensors of its own to calculate the modulated firing rate for its burner, the cooler return temperatures it would see as a result of the outdoor reset in moderate weather would cause the Munchkin’s control algorithm to assume it needed to fire at full blast, precisely the opposite of what would be needed in those circumstances.

Any and all advice is welcome and appreciated.

Mike T., Swampeast MO

Look for this article

Sorry, I don't have the link anymore, just the printout.

Comfort Division, Danfoss Sikelborg

"Design of Radiator/Convector Configurations in a One-pipe and a Two-pipe Installation"

In sum, they greatly recommend two-pipe for new installations.

"Radiant Baseboards?" I have heard of such from the UK, but the output tables seemed rather strange (I think based on their generally MUCH lower space temperatures), would require quite high supply temperature and would seem best suited to "minimalist" European interior design.