Combi Boiler System Installation Help

[Reicherb]

I've got a new polebarn with 1/2" pex tubing in the concrete slab floor. The slab is insulated underneath with rigid foam insulation. 2" I believe. The walls have 2" of rigid foam and 2" of closed cell spray foam. There will be 3 zones. primary building is 30x40x14. There are 2 smaller rooms that are 10x20x10.

There is a small bathroom that will also be the home of the boiler and a small kitchenette. directly behind the bathroom.

I plan to install a Weil-McLain AB-80C AquaBalance Combination Wall Mount Gas Boiler, 65,000 BTU (NG) but could be convinced to do something different.

I've read the manual at https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Weil-Mclain-383-100-030-User-Guide.pdf and have a few questions.

1. Do I need a DHW mixing valve? The manual says I do but it seems like with my basic pole barn setup where I'm really just looking for DHW for handwashing and with the fixtures being so close to the boiler, I don't need it.

2. I'm looking for help with circulation pumps. Is it best (maybe simplest) to do one pump per zone or do I use a single pump for all zones? Can you help me size the pump(s)?

3. I'm struggling to understand if the boiler has all of the controls and I simply connect everything or do I need some sort of external switching/relay device?

4. Am I ok to use ball valves to manually control the flow between primary and secondary loops? Why is this connection required on a condensing boiler? Does the return temp still need to be at a certain level?

5. Why would I use 2 wire zone valves vs 3 wire zone valves here? I've got 3 wire in the house.

Thanks!

 

[Dana]

I've got a new polebarn with 1/2" pex tubing in the concrete slab floor. The slab is insulated underneath with rigid foam insulation. 2" I believe. The walls have 2" of rigid foam and 2" of closed cell spray foam. There will be 3 zones. primary building is 30x40x14. There are 2 smaller rooms that are 10x20x10.

There is a small bathroom that will also be the home of the boiler and a small kitchenette. directly behind the bathroom.

I plan to install a Weil-McLain AB-80C AquaBalance Combination Wall Mount Gas Boiler, 65,000 BTU (NG) but could be convinced to do something different.

I've read the manual at https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Weil-Mclain-383-100-030-User-Guide.pdf and have a few questions.

1. Do I need a DHW mixing valve? The manual says I do but it seems like with my basic pole barn setup where I'm really just looking for DHW for handwashing and with the fixtures being so close to the boiler, I don't need it.

The DHW mixing valve is for scald protection- it doesn't matter much if the fixture is 5'away from the waterheater or 50' away. When the boiler is running at a high temperature the internal heat exchanger is close to that temp, so the first slug of water out of the domestic hot water side could be VERY hot.

2. I'm looking for help with circulation pumps. Is it best (maybe simplest) to do one pump per zone or do I use a single pump for all zones? Can you help me size the pump(s)?

Proper pump selection requires a detailed analysis of the system radiation & loads and pumping head of each zone across flow rates. That said, most systems are over-pumped, and if implemented with separate pumps that would (almost) always be true of a zone with only 200 square feet of floor area. If you're going to punt, use a single ECM drive smart pump adequate for the pumping head of the 1200' (30' x 40') heating zone, with zone valves (and maybe even flow balancing valves for limiting the flow in the lower head smaller zones) for zone control.

3. I'm struggling to understand if the boiler has all of the controls and I simply connect everything or do I need some sort of external switching/relay device?

It sounds like you're in way over your head. Read the manual as your bedtime story for a month or two until you understand it completely.

4. Am I ok to use ball valves to manually control the flow between primary and secondary loops? Why is this connection required on a condensing boiler? Does the return temp still need to be at a certain level?

The flow on the secondary (radiation loops) will vary, depending on how many zones are calling for heat, and that flow may not be appropriate for the radiation- you have to do the math carefully when pumping direct, and it gets more complicated when there are multiple zones. There is a minimum flow required for the boiler to not flash-boil yet needs to be low enough to not prematurely erode the internal plumbing of the heat exchanger and operate at a high enough delta-T for good efficiency. On p35 of the manual the AB-80 needs to always run at least 2.9 gpm but never more than 7.9 gpm. (A flow of 2.9gpm for a 200 square foot radiant zone would be overpumped x 5.) With a properly sized primary pump and a hydraulic separator to limit the influence of the secondary (radiation) flows and primary (boiler) flow the correct range of operating flow through the boiler will always be met.

I haven't read the manual for that boiler, but you should. Most manufacturers will recommend primary-pump sizes hydraulic separation configurations. The AB-80 has an internal 3-speed Grundfos that will probably work as primary pump, but is unlikely to work as a direct-pumped system pump on your system. YOU HAVE TO DO THE MATH. Hydronic heating is way more than just another plumbing exercise!

5. Why would I use 2 wire zone valves vs 3 wire zone valves here? I've got 3 wire in the house.

Thanks!

Two wire zone valves burn a small amount power to stay open, and close via a spring, and are simpler beasts than 3 wire versions. But it really comes down to what it compatible with your intended thermostats if controlling the valves directly from a thermostat. Pretty much all 3-zone zone controllers can handle either type of zone valve, and work with almost any thermostat.

If you need/want to pump direct (no primary/secondary) going with a fire-tube heat exchanger type of combi works, but that will probably still require over-pumping the smaller zones when just one zone is calling for heat. The Lochinvar Noble series isn't terrible, and have a good turn down ratio. The smallest Noble combi (the -110) has a minimum flow requirement of 1.0 gpm at low fire, but can handle up to 17 gpm, and has much lower pumping head than the AquaBalance. This is pretty typical for fire-tube boilers & combis (there are others that would work.)

 

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[Fitter30]

How mant feet of pex number of loops and lenghts?

 

[Reicherb]

I appreciate the help. I agree that I'm currently in over my head but will get a handle on everything before moving forward. I did the same with a boiler in my house a few years ago. It's working great. You gave me a great deal of help then as well.

The mixing valve makes perfect sense now that you explain it.

Page 35 of the manual tells how to determine the required flow. I can't recall how to determine the heat load. I did that some time ago when selecting the boiler for this building. Is there a harm to over pumping as long as I don't exceed the 7.9gpm?

I don't see where the manual talks about how to wire the zone valves and thermostats when an additional circulator is used. I suspect that might be because there is one built in. As you stated, I suspect the built in one isn't enough.

I have read the manual cover to cover once and bounced around looking at specific areas several times. I've been sitting in a hospital for 25 days with my son who has a heart condition. My level of focus varies from day to day...

 

[Reicherb]

There are 10 loops. The loops are all roughly 200' They were done by the contractor the built the building. Here are some images. Loops 2 and 9 will not currently be heated.

 

[John Gayewski]

To size the pump you need an accurate heat loss calc. By zone. That determines the gpm you need. It will also determine whether you want to use ps vs one pump.

 

[Reicherb]

To size the pump you need an accurate heat loss calc. By zone. That determines the gpm you need. It will also determine whether you want to use ps vs one pump.

Can you elaborate as to how I should determine that? The building is very tight. Insulated doors and windows. If I close the doors and there is a large temperature change outside, it will be several days before the inside matches the outdoors.

 

[Reicherb]

I calculate the head load of the main building to be 33,000. It has 6 loops so 5,500 per loop. Each other room has a single loop that are also 5,500 each. 44,000BTU as the total load.

Do I use 33,000 / (20x500) to determine the flow? I assume that the correct because it's all the same zone. That puts the flow at 3.3gpm for the main zone. and .55gpm for each other zone. When all 3 are on, I need 4.4gpm.

Does that all sound correct?

I'm not sure where to go from here to determine the if the built in pump will suffice or if I need a bigger one. We're looking at 1600 linear ft of 1/2 pex.

 

[Reicherb]

If I'm reading this site correctly, 1/2 pex with 200' loops has 6.oft of head.
https://www.pexuniverse.com/how-size-circulator-pump

I would need a pump that can do 4.4gpm at 6.0ft of head.

If I'm reading the chart on page 37 of the manual, the built in pump is just slightly too small. Since it's a pole building (shop/garage) where perfect comfort isn't an issue and I like simplicity, would the built in pump get the job done?
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Weil-Mclain-383-100-030-User-Guide.pdf

 

[Fitter30]

Taco 007E pump would handle your gpm load for either 8 or 10 loops. 1600' pex = 56,000 btus/ 2000' = 70,000 btus

 

[Reicherb]

Taco 007E pump would handle your gpm load for either 8 or 10 loops. 1600' pex = 56,000 btus/ 2000' = 70,000 btus

Can you help me understand how you came to those numbers?

 

[Fitter30]

1/2" pex floor radiant puts out approximately 35 btus per foot. Boiler your thinking about using 65,000 btus which with 8 loops 200' per =.81 gpm per or 1 gpm per 10,000 btus boiler flow rate. Taco 007E pump uses a ecm motor is a little large but it only pulls 44-54 watts
https://www.pexuniverse.com/how-size-circulator-pump

 

[John Gayewski]

You cannot use the circulator that comes with the boiler for your zones. It is meant for the primary loop. There is too much head going through the boiler for it to be of any use out in the zones.

 

[John Gayewski]

I would figure the heat loss for each zone and size the circulators accordingly. I would use three circulators vs zone valves.

If there is one circulator that can do the tiny zones and the big zone then use one, but I'm gonna doubt that.

If you buy a variable speed circulator be aware that it WILL shorten the life of the circular.

 

[John Gayewski]

What is this pole building for?

 

[Reicherb]

It's a shop and storage building. I work on vehicles. Do hobby woodworking. Store my boat. the kids do batting practice, etc.

I think I did calculate the load above.

Does the Taco 007 E not work no matter which zones are calling for heat?

If I do 3 pumps, do I need to do something to ensure no flow if there isn't a call for heat?

 

[John Gayewski]

You just need a primary loop of piping. The zone circulators come from that.

 

[Reicherb]

You just need a primary loop of piping. The zone circulators come from that.

Can you find an example drawing of what that would look like?

 

[John Gayewski]

I would choose any one of the three pictured.

 

[Reicherb]

I was envisioning the bottom one without the separator. Do I not need an expansion tank in that design?