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Old 01-10-2010, 11:48 PM   #1
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Hot Water Heat Layout Question


I have a 100 year old house (it seems, at least...) and have just added a sunroom and replaced the old boiler with a new Weil-Maclain, also adding an indirect fired domestic hot water heater. The sunroom will have radiant floor heat from pex tubing just above the subfloor (RHT end turn boards with ripped plywood infill,) when I can get it to run.

Yesterday, we hooked up the pex and a new circulator for that loop, including a 140 deg mixing valve and a check valve. It is connected up as Priority 3 to the furnace, and has its own thermostat out in that room. When we fired it up, I find a couple of oddities:

1. When the water heater calls for heat, it has priority, and the rest of the house waits. I understand that. However, the same is true of the main system circulator. When it runs, the new room waits. Only one of these circuits runs at a time? Can't the new room feed off of the main circuit?

2. When I got into the programming of the W-M, I found that I could have the main thermostat run both circulators. However, when I do this, I get no heat to the new system. The new sunroom loop circulator is a Taco 007, while the main is an 0014, (as is the DHW one.) They are all on the return legs of their circuits. The mixing valve is on the hot line from the boiler with its cold feed teed off the sunroom return right after its circulator.

3. Turning off the main circuit at its thermostat and turning on the sunroom one runs just the SR circuit. Should its boiler temp settings be set down to 140 degrees or just let the mixing valve worry about dropping the temp in the SR circuit.

4. When I do run as in #3, (with the system still cold,) it drops the return temp way down, and when the main circuit comes on (180 deg supply) the controller trips out on "supply >58 deg higher than return."
5. I had some pros install the furnace and water heater, and it's been running for a month or so, but not heating the house adequately, as we did take out a big radiator from the kitchen, thinking the pex from the adjoining sunroom would make it up. I'm not there yet, and it was -10 here last night, so I sure would like to get this pex heated up!

6. The pros left the main circuit as one loop from hot to cold furnace ports with the one main circulator. The schematics in the Installer's Manual shows the two lines from the furnace coming to another complete loop with a separate circulator in it, with tees into the loop not more than a foot apart. Do I need to add another circulator to this main loop? What is the logic of having a secondary loop?

Thanks for any help, guys!

Spook

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Last edited by spook74; 01-11-2010 at 02:32 PM. Reason: Corrected bolded reference to sunroom circulator.
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Old 01-11-2010, 06:08 AM   #2
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Hot Water Heat Layout Question


Sounds like the mixing valve is also piped wrong.

The purpose of primary secondary piping. Is to ensure that the boiler has enough water flow through it.

Sounds like it doesn't with our sunroom loop, since your getting the 58 degree rise error

Can you post a pic of the piping at the boiler.

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Old 01-11-2010, 02:22 PM   #3
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Originally Posted by beenthere View Post
Sounds like the mixing valve is also piped wrong.

The purpose of primary secondary piping is to ensure that the boiler has enough water flow through it.

Sounds like it doesn't with our sunroom loop, since your getting the 58 degree rise error

Can you post a pic of the piping at the boiler.
What was the verb in your second comment? (Doesn't what?)

How is the mixing valve wrong? It is on the hot feed line coming off the furnace, with the cold line coming from the loop return.

I have a jpg of the circuit as installed. Here's a link:
http://picasaweb.google.com/lh/photo...eat=directlink
See anything wrong?

Thanks for the feedback!

Last edited by spook74; 01-11-2010 at 02:27 PM. Reason: Adding schematic!
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Old 01-11-2010, 02:44 PM   #4
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Hot Water Heat Layout Question


Quote:
Originally Posted by spook74 View Post
The new sunroom loop circulator is a Taco 007, while the main is an 0014, (as is the DHW one.) They are all on the return legs of their circuits.
Do the pumps need to be the same size?

Putting them on return legs seems wrong to me, (as an aircraft gearbox engineer.) When I try that, I get cavitation from the pressure drops upstream of the pump. Shouldn't they be on the supply side to keep the bubbles compressed?

Thanx,
Spook
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Old 01-11-2010, 03:39 PM   #5
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Hot Water Heat Layout Question


On hydronics. Circulators(they are NOT pumps, and can not pump fluid) are usually best on the supply side of the boiler, to prevent compression on the micro bubbles.

Your system NEEDS to be piped up as a primary/secondary system. Your radiant loop will NOT flow enough for the boiler to operate. And often, the radiant loop will have less the ¼GPM going back to the boiler.

I would call those plumbers back. And have them pipe it up properly. As it is described in the install manual. Why spend good money to get that kind of bad work.

In the second paragraph. Its doesn't have enough water flow through the boiler.
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Old 01-11-2010, 04:27 PM   #6
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Quote:
Originally Posted by beenthere View Post
On hydronics. Circulators(they are NOT pumps, and can not pump fluid) are usually best on the supply side of the boiler, to prevent compression on the micro bubbles.

Your system NEEDS to be piped up as a primary/secondary system. Your radiant loop will NOT flow enough for the boiler to operate. And often, the radiant loop will have less the ¼GPM going back to the boiler.
In the second paragraph. Its doesn't have enough water flow through the boiler.
Ding! Ding! Ding! That makes a lot of sense. Thanks.

Yes, when the system was switching over from powering the house to the sunroom (if I turned down the house thermostat,) it would leave the furnace off for quite a while as it mixed the 180 deg water with the return water until it got down to the 160 deg setting for the radiant side. Then when it did come on, it would trip out, probably due to the low flow.

The installation manual shows the circulators all on the return side. It they were on the supply side, they would leave the lowest pressure in the system right upstream of there, in the boiler. I think you have the right idea, but the place you would not want the bubbles is in the boiler, I presume.

Last question: (HA!) :-) How do you control this many circulators? The W-M furnace will drive three, which I presumed to be the DHW as Priority 1, the main loop as Priority 2, and the sunroom as Priority 3. If I separate the boiler and main loop functions, I'll need another control. How do I do dat?

Thx!
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Old 01-11-2010, 04:49 PM   #7
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Hot Water Heat Layout Question


Your reply also made me question these plumbers' choice of pumps too. (They did not impress me as being familiar with hydronic systems!)

They had me match the Taco 0014 that was supplied with the furnace for the new indirect water heater loop, which is right beside the furnace on 1 1/4" lines. The minimum on the table in the manual shows 7 gpm, 40 deg temp rise, 3.6 feet boiler head loss, 1.3 feet piping head loss, and 1 foot water heater loss. At 5.9 feet head loss, the 0014 would put out almost 28 gpm! The W-M Gold Plus 40 water heater only needs 9 gpm. The Taco 007 would still do 13 gpm!

I also do still have the circulator we removed from the old system, which I could wire in as a secondary loop pump, (it's old job,) if I knew how to connect its control wiring up. (Should I just leave that loop running all the time?)

Thanks,
Spook

Last edited by spook74; 01-11-2010 at 05:11 PM. Reason: Add water heater head loss
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Old 01-11-2010, 04:49 PM   #8
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Hot Water Heat Layout Question


Myself. I prefer to use a circulator relay(switching relay). Like the Taco SR3.

The 0014 that came with the boiler, is just used to circulate water when any of the heating zones come on. The indirect is hooked to the priority 1. So only it gets heat during a domestic call.

I also use the built in outdoor reset function to control water temp for heating.

Your mixing valve is really only need when the outdoor temps drop low enough that 140 won't heat your other heating zone.

You can also set it up, to do a min water temp of 160 any time it gets a heat call. if you want your house to heat up a little faster during the milder temps of winter.
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Old 01-11-2010, 05:03 PM   #9
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Hot Water Heat Layout Question


The 0014 on the indirect loop. May end up having a short life span.

3.6+1.3+4.9=9.8' of head.
A 007 will move 4GPM. And a 0014 will move 22.5GPM.

Probably a 008 should have been used for the indirect. it would give you 8GPM. Largest size would be a 0011, at 10.5GPM.
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Old 01-11-2010, 05:33 PM   #10
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Quote:
Originally Posted by beenthere View Post
The 0014 on the indirect loop. May end up having a short life span.

3.6+1.3+4.9=9.8' of head.
A 007 will move 4GPM. And a 0014 will move 22.5GPM.

Probably a 008 should have been used for the indirect. it would give you 8GPM. Largest size would be a 0011, at 10.5GPM.
The 4.9 came from 3.6 +1.3. Plus 1.0 for the water heater itself gives 5.9. Did I miss something?
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Old 01-11-2010, 05:38 PM   #11
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Hot Water Heat Layout Question


I didn't know you had added them together. I thought you were listing know head pressures for the entire pipe system tank and boiler.
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Old 01-12-2010, 02:17 AM   #12
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Quote:
Originally Posted by spook74 View Post
The installation manual shows the circulators all on the return side. It they were on the supply side, they would leave the lowest pressure in the system right upstream of there, in the boiler. I think you have the right idea, but the place you would not want the bubbles is in the boiler, I presume.
I found an interesting tutorial on this at
http://www.healthyheating.com/Page%2...rc_dynamic.htm where (a number of slides in) he talks about pressures up and downstream from the circulator, and if system pressure was not sufficient, the pump would cavitate. Lower local pressure also lowers the boiling point of the water, so if this is occurring in the boiler, it will boil!

This then suggests that putting them on the return will keep the local dynamic pressure in the boiler up, and the boiling point of the water there higher.

I went through the calcs on the sunroom circuit, and came up with about 2.5 psi (6 feet if head) pressure drop in the 250 feet of 1/2-inch pex and maybe another foot in the 30 feet of 3/4-inch copper leading over to it, considering some for the elbows, etc., at about 0.5 gpm flow, at .91 ft/sec velocity. Even the Taco 007 is way oversized. I'll check their website for something smaller.

I guess I still don't undertand why the sunroom did not heat with that big honkin' pump on it when the main circulation pump was running too. It should have sucked from that circuit and modulated the temp down with the mixing valve. It seems like ALL of its flow was running across the mixing valve, and it didn't let any hot water in to warm it up.

Thanks for all the help!
Spook
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Old 01-12-2010, 02:47 AM   #13
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Hot Water Heat Layout Question


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Originally Posted by spook74 View Post
I guess I still don't undertand why the sunroom did not heat with that big honkin' pump on it when the main circulation pump was running too. It should have sucked from that circuit and modulated the temp down with the mixing valve. It seems like ALL of its flow was running across the mixing valve, and it didn't let any hot water in to warm it up.
I may be on to something. The mixing valve is hidden up in the rafters and oriented so you can't see the numbers on the knob. I think I had it all the way closed! I'll run it (with the main circulator) overnight and see if it warms up some. When it is on, it sets the main circuit setpoint down from 180 to 160 degrees, so the house may cool some overnight, but if the sunroom heats, it will be worth it!

Spook
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Old 01-12-2010, 06:15 AM   #14
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Hot Water Heat Layout Question


Circulators move water in a system by creating a pressure differential from there inlet side to their outlet side.

The small pressure decrease from having a circulator on the supply side of the boiler helps to move micro bubbles out of the boiler.

Since the pressure in the boiler doesn't go below 0PSIG. The boiling point of the water is always above 212°F.

Your Ultra should be factory set to a max water temp of 190. So you would never boiler the water in it with the circ being on the supply side.

Even if the mixing valve was set to min. Turning it to max setting won't circ enough water once the mix water is at temp. It will bypass the boiler, and flow will be too low.

Another question. Why are you setting the radiant loop boiler temp to 160?
You lose some efficiency from the boiler. Since you have gone above a water temp that will allow the boiler to condense combusted gas to absorb that heat. A higher GPM at a lower water temp through the loop would get you the same amount of heat, and a better efficiency from the boiler.
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Old 01-12-2010, 09:23 AM   #15
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Quote:
Originally Posted by beenthere View Post
Even if the mixing valve was set to min. Turning it to max setting won't circ enough water once the mix water is at temp. It will bypass the boiler, and flow will be too low.

Another question. Why are you setting the radiant loop boiler temp to 160?
You lose some efficiency from the boiler. Since you have gone above a water temp that will allow the boiler to condense combusted gas to absorb that heat. A higher GPM at a lower water temp through the loop would get you the same amount of heat, and a better efficiency from the boiler.
Neither max nor min position worked to keep flow into the radiant circuit, with both the main and radiant circulators running. Max would start to flow, and the pipes started to heat, but when I checked ten minutes later, (with no change in the boiler,) it was cooling back to ambient on the hot side.

Because the radiant loop flow rate is so low, (0.5 gpm,) I am now running both the main and radiant circulators when the radiant calls for heat, (to maintain the boiler flow.) This approach keeps the rest of the house warm. However, if I use >160 for that boiler setpoint, the rest of the house will now overheat with its circulator running all the time. (This is just until I get a primary/secondary loop set up to allow just the boiler to circulate, and while I work to get the radiant circuit running.)

Gerry

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