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[bub147]

Hi all.  Ive been reading many of the posts here and am sure Ive stumbled on the right place.  I just got a pretty large OWB and and starting the system design / install.  I have a new 1100 SF shop with 16ft. ceilings that has 5/8 " Viega Pex installed 1' OC. that is about 30 ' from the OWB.  I ll install a water heated Modine as well for quick heat as well.  The shop will have a small HW heater with a Plate HX for when the boiler is on. 

The boiler will also be used to heat my house which is about 150' from the OWB.  I want to install an air/water HX in my hot air furnace and use the fan of the furnace to distruibute the heat. I will also be installing a Plate HX for domestic HW in here for when the boiler is running .  My basement will need heat too so I was thinking a small modine or a couple sections of baseboard.

I have many questions but Ill start with the largest which is what size UG pipe should I be putting in?  My gut is saying to me 1 1/4" but I dont know for sure.  I certainly dont want to undersize and have to do it twice, but I dont want to end up with huge pipe that will require more pump for no reason. 

What about air / water HX sizing ?  Do I just get the same BTU rating as what my furnace outputs or different?

What about pump sizing or placement ?  Should I have one pump that delivers water to the building then a second to push through the radiant and a third to go to the modine?  Or just one big pump?  How would this be sized?  As a side note, the boiler has serveal inpout and output connections so the shop and house will be on seperate loops.

Ive got many more questions on controls etc. but Ill leave it at that for today.  Thanks for the help and look forward to being part of this site and forum.

~Seth.

[muffin]

don't know about pex size, I would match what ever is on the boiler, at least to the garage and house.  It doesn't sound lie you have a lot of heating devices so I would think two loops with a pump each would be fine.  One for the shop stuff and one for the house stuff.

[RSI]

Larger pipe will require a smaller pump, not larger. Really the only reason not to go with the larger pipe is the cost.

For the shop, I would pump the water from the boiler through the modine (need to make sure the modine can handle the flow without restricting too much) and back out and then the floor will need it's own pump on a secondary loop. For heating the DHW in your shop, you may want to use a sidearm on that one instead if it won't be used every day. Otherwise the water in the tank will cool down.

Usually it works best to size the heat exchanger to the furnace plenum and not worry about btu ratings on them. (unless you have a really small plenum)

[bub147]

RSI

I did a rough skketch of what I think you are telling me.  If I understand you correctly the HW from the boiler needs to run through the modine first then hit a second pump and run throught the floor.  My question would be that if I set the floor temp higher than the modine ( when the shop isnt in use for example), the themocouple on the modine will kick it on when that wouldnt be the intent.  Maybe I am missing something??  I want to be able to run the radiant heat without necessarily running the modine, as I would use it just for quick heat.

[RSI]

No, the floor loop would just have two tees in the line as close together as you can get then. When the floor isn't calling for heat all the water will just bypass completely. If you don't want water always circulating through the modine you would need to do the same thing with another pump for it.

[willieG]

thermo pex  says you can push water through their 1.25 inch pex at 6.6 feet per second =17 gpm anything after this flow starts to erode fittings prematurely

pex charts put the flow rate at 4 feet per second = 11gpm

your 4 floor loops (5/8 pex) will require between 2 and 3 gpm for each loop for a total of 8 to 12 gpm when calling for heat. if you wish to use a modine and a plate exchanger at the same time you will require a pump that can deliver close to 15 gpm likely (or as suggested, 2 pumps)
you could use a header system and put the modine on line with your plate exchanger. you could let the plate exchanger run all the time (to complete your loop to and from teh boiler) you could also if you wish not to put water through your modine, use a zone valve on a thermostat, and a zone valve and pump on a thermostat for your floor heat

just suggestions there are likley a few other ways as well

along with any system design you choose, you will need to factor in your head loss for that system

remember as you increase the velocity you will also increase the friction in the pipe

[willieG]

let me first appologize for my error in the floor loops, they will require 2 to 3 gpmm but once the floor is warmed up likely only 1/3 or less water will need to come from the boiler, the majority of the makeup water will be coming from the return line from one of the other appliances (that is left open to keep water circulating) So you would likley still have 7 or 8 gpm to run the other "appliances"

so 11 gpm would likley be sufficient for your  floor, a modine and a plate exchanger

sorry for any confusion i have caused

[bub147]

Understood and thank you.  I think what you are saying re: the head loss is that I want to make sure that Im getting an actual 11 GPM through the pipes and not just a pump that is rated for 11 GPM.... ie factor in losses.  You brought up a point which I didn’t consider but will pose now ... that is if the system requires +/- 11 GPM using just one primary pump and zone valves, what do you think would be the requirements if I had a pump at the boiler to circulate out to the building then separate pumps for the modine and the floor loop ?  I would assume they could be smaller but then again if both zones are calling at the same time, there would need to be enough flow to satisfy everything ... I am looking from an electric efficiency point of view in that I think I want a smaller circ pump that runs basically 24/7 to reduce electricity demands.  Does that make sense?

[willieG]

i think it is rsi who knows a lot about energy efficent pumps and what ones draw what power. he likley knows best but i am still a believer in if one pump can do it then i only have one pump to worry about replacing. again maybe you should talk to rsi about pumps

[Scott7m]

The energy efficient pumps are the grundfos alpha I believe.  I trust them and would have no worries about them

The system using 2 closely spaced t's is a life saver in many situations, a pump in the supply side of the first t supplies heat tp that application when need be, if it's not in use the hot water goes straight through the t's and on through the loop