will const circ really move heat from warmer to cooler rooms?

Plumbob

I read this somewhere on the Wall, and also it is reasonable in principle, that if the water flows all the time it will tend to equalize temperatures in diffrent rooms. This is because it will lose more heat in cooler rooms and less in warmer rooms.

But is this a noticeable effect, or completely negligible in practice unless one room is tropical and the other is arctic?

Specifically, we have two zones, and the baseboard zone currntly calls for heat ~20% longer than the radiator zone. Is the "equalizing effect" of constant circulation any significant help in achiving even temperatures if I combine these two zones into one? The reason I want to combine them is to get 100% circulation, which is more efficient and less noisy, and obviously that can't be done with two zones that have different needs.

I know, I should try it and see. But I thought I should ask first whether the effort is very likely to be a waste of time.

John Mills_3

I did one once...

2 story house with addition on a basement. Did constant circulation. Customer said house didn't feel right afterwards. I took a digital stat and checked every room. Every room was within 1.5 degrees of each other! He was used to hot & cold spots. Of course this only works if the guy who laid out the house to begin with did a perfect job with his heat loss calc and his radiation sizing. Obviously whoever did this house 30 years ago sure did the trick.

S Ebels

In a word

Yes

I was doing some detail work in a house we did last winter. It had Climate panel in the great room which was hardwood in front of those 2 story window walls you see pictures of. I had been there for about 3 hours when I realized I hadn't heard the boiler fire. I went upstairs and checked around and the house felt cozy warm. I shot the floor to see what was going on in different areas of the house and found that where the sun was hitting the floor the surface temp was running 95-98*F. Other places in the house were more normal. The areas in the great room that were not exposed to the sun were also cooler by about 10*. I went back down and checked the water temp for the low temp side of the system and found it was 88*. The high temp side was shut down. I worked there till late afternoon and the temp didn't drop until the sun "went around the corner". Based on that, I have to say there was a good amount of passive solar heating going on and the circulation was indeed moving the btu's around the house.

Unknown

just for the sake of arguement, could it have been simple convection from the passive solar in the great room?

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S Ebels

I wondered about that also

I don't think it was. As I was working in the house I kept watching the system temp. It didn't change as long as the sun was full on the floor. The area that the sun was striking would have been roughly 400 sq ft. and I think it was enough to maintain the btu drop in the rest of the house. The boiler didn't fire for a period of nearly 5 hours at an outdoor temp of 16-20*. The other rooms on the main floor stayed at 68-70* also. This included two bedrooms that had the doors shut. I can't conceive of any other way the heat was moving to those rooms.

This is the only house I have ever observed this in. I think that all the conditions for the heat transfer to happen are present in this particular home. The HO indicated that he had noticed the same thing on bright sunny days. You would have to monitor the actual temp of the loops going into and coming back from the sunny location in order to actually determine if it was happening.

Ron Schroeder_2

You wouldn't have heat transfer from one room to another unless the loop temperature is lower than the temperature of the hotter room. Remember, heat travels from hotter to cooler so if the loop temperature is hotter than a room, heat can't go from the room to the loop.

If the radiators are in direct sunlight, they could act like solar collectors and that could raise the loop temperature and allow that heat to transfer to other rooms.

Ron

jerry scharf_2

yes, but...

Jim,

Let me restate the case to make sure I have the picture right. Zone A has baseboard, and I assume it covers a number of rooms. Zone B has radiators, and controls some other rooms. You want to combine the two zones into one.

Why do you want to combine the zones? Baseboard convectors and standing iron radiators have very different heating characteristics and respond differently as the supply temperature changes.

What controls the heat to the two zones right now? If it's a pair of thermostats, then I see no good way to combine them. If you wanted to change to TRVs on each radiator and constant circulation on the radiator zone, that will add comfort. Going to constant circulation on the baseboard would be more problematic, and may be difficult depending on the plumbing of the system.

We would need many mor details before any guess could be made of the difficulty and benefit of the move you are considering.

hope that helps a bit, jerry


jerry

jerry scharf_2

what were the controls

Steve,

I'm curious what the controls were for this. Most control systems I know of make the assumption that the heat is flowing from the boiler to the rooms. This would lead them to shut down the water flow to the room that had the solar gain.

Also, you hit the nail on the head. You had the hot floor to get sufficient delta T to push BTUs at a reasonable rate. In the air to air or MRT (mean radiant temperature) to MRT cases you may have rooms 5-10 degrees different. Then you you have to pay the R value of going into the tubes on the warm side and out of the tubes on the cool side. In the real world, this is going to make for very slow heat flows.

Even in your case, this is only going to operate in the cases where the overall load is very low. Once the boiler kicks in, the ability to do what you saw will most likely go away.

I would submit that in all but a few cases, using a hydronic heating system to move heat between rooms is hard. Air mixing can do this job and I am using that in my soup to nuts project. It has it's own fun.

jerry

Plumbob

> Why do

> you want to combine the zones?


To run the circulators all the time. I can't do that with two zones that have different requirements, so my question was, will the requirements actually even out if I run const circ.

> What controls the heat to the two

> zones right now? If it's a pair of thermostats,

> then I see no good way to combine them.


Why not? I can run both circulators and the boiler with one thermostat. (I can't use a single circulator because one zone has 3" pipes and the other 1/2" pipes.) Alternatively I can have const circ in one zone and thermostat-switched circ in the other zone. The wiring is easy; whether it will produce steady temperatures is something else.

> If you wanted to change to TRVs on each radiator and

> constant circulation on the radiator zone, that

> will add comfort.


Yes, this would be the better (but more expensive) solution.

> Going to constant circulation

> on the baseboard would be more problematic, and

> may be difficult depending on the plumbing of the

> system.


I don't follow. To get constant circulation, I just need to wire the circulator directly to power. The plumbing remains the same.

George_10

Just an off the wall question?

What would happen if you put a timer on the circulating pump and run it for a certain length of time every hour.

What would be the result? If you have done so could you tell us what your experience was.

Like I said just an idle question.

Plumbob

why

Why?

PS All questions posted here are "on the Wall" questions.

Daniel Moore

Life expectancy of a circ pump

What is the life expectancy of a pump if it is continuously running? Does it still last for years if it is properly oiled? If so there wouldn't be much need to run it on a timer.

jerry scharf_2

my answers

> > Why do you want to combine the zones?

>

> To run the circulators all the

> time. I can't do that with two zones that have

> different requirements, so my question was, will

> the requirements actually even out if I run const

> circ.


No. What are you looking for by using constant circulation? Do you have noise problems? Do you have uncomfortable living conditions? Something else? Read below before answering.

>

> > What controls the heat to the two

> > zones right now? If it's a pair of thermostats,

> > then I see no good way to combine them.

>

> Why not? I can run both

> circulators and the boiler with one thermostat.

> (I can't use a single circulator because one zone

> has 3" pipes and the other 1/2" pipes.)

> Alternatively I can have const circ in one zone

> and thermostat-switched circ in the other zone.

> The wiring is easy; whether it will produce

> steady temperatures is something else.

>


Ask yourself this: How am I controlling the heat in the rooms? If you run constant circulation, you either need to control the flow to the emitters or you need to control the water temperature. The thermostat switching on and off can be seen as doing either of these, with the mass of the rooms acting as an integral function to smooth the swings.

Now ask yourself this: How am I controlling the heat for two different types of emitters with different output characteristics. You will either need independent temperatures or flows for the two classes. To produce different temps, you will need either controlled mixing valves or injection pumps. To vary the flow you need either mechanical or electronic proportional valves driven from a room sensor.

As I have said any number of times, outdoor reset is not a primary control strategy for room heat, it's a secondary optimization of efficiency and comfort. Something has to read the room temperatures and adjust the BTUs in for the loads and the emitters. Lots of ways to do this,

> > If you wanted to change to TRVs on each radiator and

> > constant circulation on the radiator zone, that

> > will add comfort.

>

> Yes, this would be the better (but more

> expensive) solution.

>

> > Going to constant circulation

> > on the baseboard would be more problematic, and

> > may be difficult depending on the plumbing of the

> > system._BR_

>

> I don't follow. To get constant

> circulation, I just need to wire the circulator

> directly to power. The plumbing remains the

> same.




Once again, how do you control the heat in the rooms heated by the baseboard? Loop baseboard makes it hard to do TRVs on a room by room basis. The same is true for radiators, but it's more hopeful that the radiators aren't in a single loop.

jerry

S Ebels

Jerry

The control/boiler system was a Vitodens which, of course comes with its own control. At the time I was looking at the system it target temp for the floor loop was 84-85*. The water coming back from the sunny area was warmer than that, hence it kept the system temp elevated enough that the boiler did not fire. The high temp loop was not on line at the time so the boiler was not maintaining temp for that. The mixing valve was in full bypass position re-routeing all the return water directly back to the floors.

Leo G_99

oh Jim

if the wiring is easy to do, and the time and cost isn't much, I say try it! I find that sometimes things work in the feild, even though they won't in the lab (and vice-a-versa!)!

Just keep us informed on what happens!!!

Leo G