Primary/Secondary with Mod-Cons (Part III)

Mike T., Swampeast MO

No flow control valves yet considered. Do you mean to ask why the estimated flow for that master bath zone is so much less? Check the pump curve against the head loss in a <I>single</I> circuit of the specified length and you should see.

Mike T., Swampeast MO

Attached are the revised parameters. I changed the tube spacing in the garage to 12" (vs. 6"), but left the ¾" @ 12" spacing in the bulk of the basement.

While I've made my job ever more difficult by using such a complex system, such has a purpose as I tried to consider problems that typically occur in the real world.

The master suite is a good example. It's in a sort of wing with a relatively high ratio of outside walls to floor area. There's a gigantic window to the front (south), a fair number of other smaller windows and a big window/french door combination in the sitting room facing north leading out to the terrace. Loss per square foot is a bit higher than the norm for the common areas. That's not too much of a problem, but the homeowner insisted on a relatively plush carpet for the master suite (but you did manage to keep it and the pad's resistance to the flow of heat down to about R-2).

I won't even bother to attempt to model the system at design conditions with a boiler sized closely to the calculated loss. Why?

Because it is IMPOSSIBLE for anything but a massively oversized boiler to have sufficient output to maintain the supply temperature required for the master suite with all zones calling.

Again, why? Because the remaining "high temp" zones will be greatly oversupplied with heat thus increasing their output significantly. The big zone (common space) alone will find its output jumping from the required 22 btu/hr/sq.ft to at least 33 btu/hr/sq.ft and will be trying to dump at least 61 mbh into the space when it only needs 41 mbh! Any rationally sized boiler will be simply unable to maintain the temp required for the master suite (147°F at design conditions) until other zones have been satisfied and cease their call for heat.

In the next day or two I'll post drawings of the system at 50% of Manual J loss using various forms of primary-secondary. I'll even try to combine some of these zones under a single circulator sub-divided via zone valves. While a reasonably sized boiler [should] be able to maintain the highest temp required in the system, you will find that it cannot possibly supply the zones proportionate to their share of loss.

p.s. I again offer my services virtually if not totally free-of-charge to a good heating contractor or extremely informed homeowner who wants to use Warmboard™, FHVs and a Vitodens 6-24. In my mind at least that combination can result in the most comfortable and most efficient heating system ever created.

Dave_4

Radiant ceiling

It wouldn't be a bad idea to consider a radiant ceiling for the master bedroom. It would be more responsive if anyone down the road ever decides to use a whole house setback. Wake up with radiant on the face... wait, that sounds entirely wrong somehow.

Mike T., Swampeast MO

At the risk of jumping ahead...

...this is not what I would personally use, but I do believe it reasonably representative of thoughtful design based on typical practice.

The problem I see however is that people are trying to apply "typical practice" to MODULATING boilers. SUCH IS IMPOSSIBLE IF YOU WANT TO MAXIMIZE BOTH EFFICIENCY AND COMFORT!!!! One or the other will suffer--ALWAYS--unless you also have modulating flow.

The dead men with their coal-fired boilers driving gravity-driven hot water FULLY understood modulation. The dead men who designed naturally sub-atmospheric vapor steam systems produced the pinnacle of design--EVEN BY TODAY'S STANDARDS!

To understand how to use mod/cons to their best advantage we must look BACK to the days before wall thermostats existed.

I have said this before and will shout from the highest mountain that on-off wall thermostats are detrimental to both efficiency and comfort and only exist because of cheap (in every sense of the word) design.

hr

just say no, to

radiant and "plush" carpets. Especially on a high load bedroom like you indicate. Unless you can prove you can meet the load with reasonable, below 140F supply, temperatures I'd pass on the radiant. In that room anyhow.

That pad and carpet really keeps the heat in the plywood, and I had some pretty smelly foam pad issues with those high temperature rubber staple up/ carpeted room applications.

Panel rads or baseboard offer a better and much faster heat emitter for those rooms.

hot rod

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jp_2

got me confused.....

"""I won't even bother to attempt to model the system at design conditions with a boiler sized closely to the calculated loss. Why?

Because it is IMPOSSIBLE for anything but a massively oversized boiler to have sufficient output to maintain the supply temperature required for the master suite with all zones calling. """

to me a modeled system is the basis for the design of the load, don't really see a big difference between modeling and designed heatloss other than a design would have a little higher load than the model.

are you planning sequencing of zone valves to 'keep up with the load'? I don't see your logic here?

also how do you plan to arrive at all those different zone temps with multiple zones calling?

how would your system deal with a cold start? power outage mid winter?


i agree with hot rod on carpet, ceiling or panel rads no floor heat.

edit:
why no floor valves here? or am i missing something? what will control zone valves?

Unknown

Mike, you are confusing Water temperature with boiler output.

These are two nearly entirely unrelated concepts, for one. It's temperature differential and flow that relates to output, not water temperature.

For two, If your thoughts are correct with the over-output of other areas relative to the single high intensity demand on the system, then you have no problem; they will shut off their demands much more quickly do to this overflux of heat and thus preserve output, overall, for the master bedroom. On average, no problem, except for the crappy heating characteristics of the lesser need zones having to cycle so much.

What a system with a spread that large the big issue is one temperature mixing or two.

jp_2

no flow controls?

in your other post you mentioned no flow valves.

then how do you control flow? as in the master bath?

Mike T., Swampeast MO

then you have no problem; they will shut off their demands much more quickly do to this overflux of heat and thus preserve output

Didn't I say that?

Water temperature is however linked to boiler output via the heat transfer of the emitters. If the emitters are giving off full boiler output (as could certainly happen in this system) some zones will be starved and others over-supplied with those starved only seeing sufficient temperature after some of the over-supplied zone(s) are satisfied and cease circulation.

What I plan to show is that such conditions ALWAYS occur in any multi-zoned system without proportional flow control.

This little exercise is certainly teaching me--I now completely understand why many think I'm doing nothing but blowing smoke when I suggest that a boiler can supply heat in just the amount required to counter the loss of a real-world system. Ain't never gonna' happen in "American-style" systems.

jp_2

flow curve

well i may have read your data wrong?

I saw the bath as having a head pressure based on tubing lenght at 1.2ft. the lo205 pump curve gives flow values at 1.2ft at arounf 5 gpm, as i see it? so i was wondering where the .75 gpm came from?

jp_2

head loss puzzle?

why between the common space and bedroom zone 2, both have same head loss, same pump but vastly different flow rates?

how are you bending the rules here?

both show head loss at 1.8 ft but one has gpm at 4.1gal and other gpm at 2.4 gal????????????

what am I missing?

Mike T., Swampeast MO

I'm wondering about one of us j.p...

One of us has no idea what happens when a single circulator supplies multiple circuits (loops).

I'm basing these calculations on the MAXIMUM head loss found among the individual circuits that make up a zone. Presuming equal tube length and reverse-return connections, the head loss through each individual circuit in the zone is considered equal.

With a given, fixed-speed circulator the more circuits in the gang the more total flow is possible because the flow and delta-p are shared amongst the circuits. The fewer the circuits the more each must bear the increased delta-p required by increased flow.

Again, one of us has no idea how circulators operate in the real world...

Perhaps it's just me off in my proportional nirvana.

jp_2

yep,

i see what you are doing....have fun

Mike T., Swampeast MO

This has NOTHING to do with what "I'm doing".

It has EVERYTHING to do with with how God made the laws that govern our universe.