Circulator pump size info request

[kansas cat]

Greetings all, I have just recently put up a new 30 x 50 x 16' pole barn shop building, and have been reading this forum for a while now and learning a lot of valuable info from you guys here. I am putting in floor radiant heat, and just finished installing 1400' of 1/2" pex on top of the insulation and am awaiting pouring of the concrete next...weather and money both being a cause of delay right now...anyway, while waiting for the slab to be poured i am researching and locating the rest of the materials for the heat system. I picked up a Rinnai RL-75il 180,000 btu LP tankless direct vent water heater that had cosmetic freight damage on ebay a while back for part of the heat supply....i intend to build a air to water heat exchanger to take surplus heat from a wood fired forced air furnace that heats my house to at least do some of the hot water creation ahead of the water heater...anyway, i have 5 zones in the slab most under 300' long with one that ended up being about 350'. I also plan to have one zone run upstairs to heat the floor in the future office room and one zone of the manifold run to a water to air heater assy that i have...if i feel its needed once done with the floor heat.
My question right now is i need to know what sizes i need to be looking for for the circulator pump, and the expansion tank. I know pump size needs to be based on the amount of pipe its going to be pushing the water thru, plus the factthat one zone and possibly the water to air unit will be upstairs makes a difference, plus the fact that i will be circulating the water about 15' thru 3/4" pex over to the furnace shed next to the new shop and thru a large radiator mounted near the ceiling and possibly a copper line wound around the furnace hot return air lines. So am estimating by the time i get the upstairs office floor lines ran and the lines to and from the furnace shed and the lines in it there willl be close to 2000' of lines plus the water to air exchanger / radiator and the air to water radiator / exchanger in the shed, plus the tankless water heater. The water will have two areas where it will have to rise to a height of about 8'...1 for the office floor and 1 for the exchanger and lines in the furnace shed.
I know this might sound confusing or complicated, but really its not, just think of it as a normal setup with a main floor and a small upstairs zone, but add a rad and coil of lines 7' above the floor level where i plan to pull some free heat into the water. The furnace shed i built esp to house the wood furnace. Its pretty much fireproof and well insulated with fiberglass. The furnace is capable of heating out home on its lowest setting...air intake shut nearly clear off since i heat with hedge wood only. I only have to add wood twice a day, morning and night. For the past 5 years now i have always noticed the air temp in the furnace shed runs about 150 degrees normally, and if it gets real cold out and i open the intake and feed it a bit more it can go well above that in there...and thats all wasted heat...i sometimes have to turn on a small exhaust fan and dump this heat outside . I figure i might as well use some of it to heat the water for the shop, and i like the challenge of designing and building stuff like this anyway. I figure heat the water as much as i can off this free hot air, then run that into and thru the tankless heater so it can finish the job if any more heat is needed or for when i am out of town etc and the wood is not being feed in.
I should add mention, the 3/4 pex going between the shed and the shop are 3' under ground in 4" pvc conduit and they will have foam pipe insulation around them to reduce any heat losses on the 12' run between the buildings. Both ends come up thru the slab so no outside exposure to them.
Sorry to ramble on here guys, just wanted to try to get ya a picture of what im building and get some of your vast knowledge back to save some trials and errors here.
Love this forum, some pretty wonderful shops on here and a lot of great ideas and tons of knowledge. Thanks so much for any info or help you can offer up.
Steve

 

[wedge40]

http://www.pexuniverse.com/content/how-size-circulator-pump

Wedge

 

[ABM1]

It doesn't matter that you are pushing water up to a different height, only the actual head loss through the runs you have and how many gallons per minute or as the heating guys refer to it as how many feet per second you need through the pipes to remove entrained air and not have water noise.

Generally you don't want to exceed four feet per second through the piping and not have less than two feet per second if I remember correctly.

Once you know how many gpm you need to flow and your head loss you can use a pump chart and size your circulators.

I just set up a wood fired hydronic system and learned a lot by reading on the forums on Hearth.com (boiler room section). Also you can learn a lot from the site mentioned above and also www.pexsupply.com

 

[kansas cat]

Well from what i can figure out on that link site, its looking like i would be about right with a 10 gal per minute pump and about 12 lbs head capacity. Unforutnatly im far enough out of my element im not even sure i was figuring that site out right...but the example numbers they used on it was actually pretty close to mine except i hac a bit more footage plus the extra exchangers / fan coils. I did not see just what to add for them, but by adding some to the basic figures i came up with 10Gal and 12lbs head. If i get a pump that can meet or exceed this capacity im thinking it should work pretty well.
Thoughts anyone?
Thank you to you two for your help and input. I will see what additional info comes in and see if it looks like i am on the right track. i have a little time yet to get it figured out.

 

[anthony666]

i wouldn't bother with scavenging heat from the house, it might help on start up but you'll most likely end up pulling heat from the shop .. keep it simple .. if you've already got the line maybe hook it up to a unit heater to take the chill out and help with recovery if the door is open

a 1558 in a loop through the tankless to get it to make hot water and another 1558 pumping water out to the floor

an etx 30 will take care of thermal expansion

 

[ABM1]

You really need to look at the pump curve charts and size it according to that.

On my system I ran my main feed line (1 inch) through a flat plate heat exchanger to make hot water and then out to my two zone system (which I'm running with two smaller circulators controlled by thermostats) that are tied in using closely spaced tees. You could also just use one main pump and zone valves if you are running separate zones.

That 1558 is a good pump from my experience and it's nice to have the 3 speed settings, I'm running that as my main pump and have been happy with the performance.

 

[ABM1]

One other thing I'll add after reading your initial post again - those lines running underground need to be separated with insulation to keep the cold return from pulling heat from your hot feed line. Also another concern is keeping groundwater away from the lines as it will quickly pull heat away and make it very inefficient. You could run a drain pipe in gravel or sand under your insulated line if you have somewhere to let it drain.

 

[kansas cat]

ABM1, the lines running between the furnace room and the shop are inside of fully water tight sch 40 PVC pipe so they should never have any water in there with them. Both the lines are insulated seperatly so should not get much temp swap between them. The 5 seperate loops in the shops floor will all be one zone as its all one room and will have 1 thermostat...at least to start off with. Once i get the interior walls and the upstairs office and storafge rooms built i might end up needing seperate smaller circ pumps and elec controls for those zones with their own thermostats.

As for pulling heat from the house or shop, i guess i am not following what you mean. The heat i will be using to heat or at least preheat the water going into and thru the tankless heater and into the shop floor is all heat that it completely wasted currently. The house is heated with its own air that is ducted into the furnace with a metal duct and goes thru the furnace and back to the house thru 2 round ducts. its fully seperate from the heat that is going into the furnace room and being wasted currently as its does nothing but make the furnace shed really toasty warm. I am just wanting to use this surplus heat for the shop as it will be to expensive to heat it on just the LP tankless heater. At almost $2.00 per gallon here for LP it would cost to much to heat all winter, and radiant floor heat would not be very good if just trying to turn it on when heading out to work on something. The wood furnace is fired all winter anyway as thats what we heat the house with primarily. The house furnace is set lower then we try to keep it with the wood heat, but if we are gone or i get lazy and dont go stoke the fire in the morning it keeps the house at a sufficient temp...basicly what i want to now do with the shop too. I just looked at a site that sells a SS loop to go inside a wood stove to heat water for domestic hot water use. I am thinking if they can heat water that way for domestic use, then why cant i also heat the water for the radiant system? Biggest thin i can see would be that it might require a constant circulation of the water to prevent overheating it in the furnace. Guess in that case i might have to leave a window open in the shop if it starts getting to warm. LOL that would ****, but we do that in the house if the furnace is putting out to much heat for the outside temp. I have gotten pretty good at knowing how much to stoke it and such depending on what the temps are going to be outside, but once in a while it warms up more then they forecast and we have to open a window or two.

Another area i am not yet clear on is the actual way the thermostat is hooked up and works a system like this. Are there special types of t stats i need to look for, and how are they wired in to control the system normally? Electrical is my least fav thiing to do and probably one of my weakest categories.
As for the 1558 pump you speak of...we are on the same track i think as i had just looked up and selected a Grundfos UPS15-58FRC 3-Spd Circulator Pump on ebay for $82 buy it now and was thinking that looked to meet the specs i need as best as i could tell after looking at that website link that was posted a bit ago on this thread.


Many thanks again for your input. Its discussions like this that help folks like me figure out how to do new things like this successfully.

 

[anthony666]

if the water temperature coming from the house, after all heat loss on it's journey, is not above the return temp from the floor it will not preheat the water before it goes back into the boiler

lets us some arbitrary numbers to illustrate;

say outlet at the boiler is 100 degrees
say return is 80 degrees
you must have over 80 degree water to impart any 'free' heat into your floor

if the water from the house is less than the 80 degree return temp it will pull heat from the return line

you could rig up some expensive fancy controls to turn off the water from the house if it falls below return temp .. but the cost of all that extra elaborate stuff negates the savings, we call it 'long payback' in the industry

those insert coils work really well, sometimes too well .. the best way to handle them is use a very large capacity storage tank to soak up the temperature or the t&p valve pops and you dump boiling water all over your shop

 

[anthony666]

you hook your low voltage thermostat to a relay box .. such as these;

http://www.pexsupply.com/Switching-Relays-443000

from there line voltage goes to the pump

 

[ABM1]

You can use the low voltage thermostats as mentioned above with a relay box or you could just run it all off of line voltage. I personally ran mine all off of line voltage even though I have both types of equipment available. My thoughts are that it makes one less thing to fail as the low voltage boxes utilize relays to switch everything (although I know these are also very good and have few problems) but they also use circuit boards which can and do burn out at times.

 

[ABM1]

I also agree with Anthony666 on needing a large storage if using a coil in the furnace or a dump zone (possibly a storage tank) to lose excess heat if you start to get too hot so it doesn't blow a relief (also a must have).