Two-temp system controls, redux

zeke

What about the 145 deg requirement for the indirect DWH? Wouldn't the outdoor reset be limited on very mild days?

What about using TRV's in lieu of mixing valves and csecondary loops?

Gene Davis_2

One more time, please

You input is requested, please, on controls and setup for a two-temperature system. I've a pro who will engineer it, but we always welcome other opinions.

Small new house, walkout lower level slab on grade with ICF walls, upper level wood framed. Total heat loss at -30F design temp 27,111 Btu/h.

Upper not feasible for infloor because of a large window wall, so will heat this floor (total 23,034 loss) with panel rads, supply temp to the rads 145F.

We'll do infloor hydronic for the walkout lower slab-on-grade level. Total 12,154 Btu/h heat loss.

How would you best pipe, Tstat, TRVs, pump, (inject?), control, etc., such a setup?

Expected boiler to be a Munchie T50 mod-con wallhung, which will do the SuperStor Ultra 45g indirect DHW tank, unless you can make a good case for something larger than the T50.

Gene Davis_2

Wow!

No opinions or input on this yet? I am amazed.

ALH_4

Mixing

You could use a Tekmar 360 controlling a 741 on a 3-way mixing valve.

Although, that setup is probably a little too fancy for a Munchkin boiler. A 356 would probably be a better match.

jp_2

I would design

so the panel rad returns fed the floor, return the coldest possible water to the mod/con.

Gene Davis_2

A 356

with a variable speed mix pump? We therefore go straight hot to the radiator side, and have an injection loop with the variable speed pump handle the cooler radiant side?

What does outdoor reset control? Is there one curve for all?

ALH_4

356

Yep. The Munchkin would run on a hotter reset curve than the 356 and the 356 would run on it's own cooler curve.

Gene Davis_2

This is fascinating.

So please help educate the dummy some more, if you would be so kind.

One outdoor sensor, right? Feeding its results to two little smarties inside, right? One being the boiler control, the other being the 356 brain that is running the mix scheme for the "cool" infloor pipe array for the lower level.

Do any thermostats have a role in all this decision-making? Do TRVs on the rads make any sense?

scott markle_2

The idea of utilizing the different temperature requirements of emitters and the delt between them makes alot of sense for condensing boilers. In a small single zone house this is a realistic proposal. It is in fact how I am heating my own home. This said calculating the actual operating delta thru the first part of this "flow" could be tricky. As is figuring true heat losses for the two areas. There is a real possibility that these estimates could be off resulting in unbalanced heating of the house. I used my own house as a lab. It worked out very well. I'm not sure I would be so comfortable implementing this for the average client though. It doesn't allow much room for error, and at this point most people are going to put a higher priority on comfort and user control than on the few extra percentage points we can get from increased flue gas condensation.

As far as the control recommendations made thus far, what about dhw? Have you considered the budarus gb 142 It comes packaged with outdoor reset and a nice 10k dhw sensor and relay. You could pipe the 356 downstream from the panel rads. in direct a return arrangement utilizing the drop in temperature but providing separate control for the slab, Does the 356 incorporate any indoor feedback? this would probably be good to have if there are any solar gain possibilities

Unknown

no, the 356 only interfaces with a mixing device and enables a boiler to fire. you would have 2 outdoor sensors. You could have a fully integrated system with teknet 4 with one outdoor sensor and indoor feedback on the mixing and the boiler, but currently tN4 is not constant circ friendly for the radiators, and that's much bigger money.

Ted_5

Have you seen this yet?

This is a multi path mixing disributor system. It comes with a 24v floating action motor for the mixed temp. It is your near boiler piping for the high temp and low temp circuit. Each port has an isolation valve and thermometer. It is ready to hang on the wall and also comes with an insulation box. Made in Germany. It can also be coupled together with the Twin model and give you a 3 temp system. I can send you more information if you are interested.

Ted

jp_2

mixing

i would use a mixing station between the two to insure proper temp down the line, to be used only when necessary. lots of ways to skin a cat.

Kevin G_3

Vision 2 control package

Look at the munchkin Vision 2 package. 1 outdoor sensor, 1 Belimo mixing valve, DHW priority, 3 outdoor reset curves,1 indirect tank sensor. will work with any T-stat input(open/close circuit). the vision 2 will tell the boiler what temapture to run. if only the radiant is calling and requires 100 degrees thats what the boiler set point will be. As higher temps are need for other zones the boiler will have it's set point raised and the mixing valve will throttle as needed to maintain radaint loop tempature.
Worth looking into for fuel savings.
Kevin Gabelmann

Kevin G_3

Near boiler piping

Both of these piping diagrams would have issue's on the near boiler piping. You need to have 5 gpm flow through the T-50m. All that would be needed is a primary loop and they would work just fine.
Kevin G