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[WoodMOJoe]

I finally got my homebuilt set on its foundation yesterday and was hoping for some input on my connections at the outdoor unit.  I will be enclosing the unit in an insulated metal shell eventually, but might run it "naked" at first to verify operation and watertightness.  It held an air test for about 2 weeks before I let the pressure off so not expecting any issues there.

I have provisions for 2 loops off the back of the boiler but will only be using one for now.  The 1" steel pipes with the blue thread caps are my returns and the 1" bungs on the lower half of the back of the unit are for supply.  Figured I would use a supply bung on the left half and a return pipe on the right (or vice versa) to facilitate tank mixing.

I am planning on putting my pump in the basement, and will be going through a 20 plate for my DHW and then a 19x20 hx that is in the plenum of my upflow gas furnace.

If my pump is in the house do I need to do anything, or make any other provisions besides just hooking the 2-1" pex lines to the respective supply and return bungs?  I do have ball valves to put on each line out at the furnace also.

Was also wondering if I should extend the steel return piping down below the level of the horizontal flue pipe, am worried about the heat it might get if the pex was above the height of the flue?

This is my first install so any thoughts and suggestions are most welcome, thanks.



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[hondaracer2oo4]

Looking good! Whats the reason for putting the pump in the house? What pump are you going with? How long of a run do you have? When you put the pump away from the unit, the water has to travel through the pex to get to the pump under only atmospheric pressure. Atmospheric pressure is 14.7 psi at sea level and you gain or lose 5 psi per 10 feet that you rise or lower from you water outlet. Lets say that you are using 1 inch pex and are 100 feet from the boiler to the pump. If your pump is going to be flowing 10gpm ahead of the pump, you will lose 5.5 psi by the time it gets to your pump. That leaves you with a residual of 10 psi which should be fine. But if you are going to be flowing 17gpm or more you will have a drop of 14.3 psi from the boiler to the pump leaving you essential 0 psi residual pressure and thus cavitating the pump. So we need to know the pex size, pump size, fittings, length of run etc and we can figure out what will work for you.

[hondaracer2oo4]

I just brushed up on the heat loss calculations etc. I looked up the 19x20 HX which is rated at 150,000 BTUs. If we plan to get 150,000 BTUs out of it with a 20 degree Delta T this is the calculation for the amount of GPM we need to move to accomplish that.

GPM= BTU/Delta T/500

So GPM= 150,000/20/500 = 15

So in order to extract the 150,000 BTUs from the heat exchanger and get the 20 degree heat drop we are looking for then you will have to flow 15 gpm. So my using the chart found at http://www.pexuniverse.com/pex-tubing-technical-specs we can see that 15 gpm through 100 feet of pex with no fittings will be 11.4. But remember that the GPM that you will flow depends on your pump size plus any restrictions after the pump such as pex length, fittings, heat exchangers etc. So anyways if you could gather the info about pex length, size, fitings, heat exchangers, and pump size we can help you figure it out.

[WoodMOJoe]

I want the pump inside just for ease of maintenance and being able to know what it is doing.

My pump in the basement will be near the lowest point of my system, the guys here told me that it should work fine.  From highest point in system to lowest point is about 5'-6' max.

Pump = Grundfos 15-58 FC
Pex  = 1"
Length = 70' one way (50' underground + 20' in basement), 140' total
I'm guessing I will have either 4 or 6 90s total, counting 2 on the back of furnace..

Here is how I picture my loop:

Furnace supply side underground to house -> Wye strainer -> Pump -> In/Out 20 plate water-to-water hx -> In/Out 19x20 water-to-air hx -> underground back to return inlet on furnace.

At this point I am really just wanting to know how to hook up my underground lines to the furnace, do I need anything besides ball valves, or should I make provisions for anything else at the outside connections.

I'm saving the inside questions for later!   

[hondaracer2oo4]

Wood,

  I just don't want to see you short change yourself with setting up the system so that it doesn't work the way it should. When I was setting up my system and really didn't have any knowledge on Delta T and friction loss etc I called manufacturers and dealers to bounce questions off of them, they were all disappointingly clueless on how to properly set up a system. They all just said "Yeah it should work" and if I had listened to them I would have gotten 40* plus degree drop return temps to my boiler. Just pitiful. 

So lets say that you have 3 90 degree fittings after the pump. They each add 5 feet of distance to your run from the friction loss. So we have 85 feet of pex after the pump. I am not sure of the friction loss that they HX add but lets call it 15 feet per device(not sure if I am even close on that) so that means we are at 115 feet of pex after the pump. The formula and all info pertaining to sizing your pump correctly can be found at http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf. I highly recommend it if you want to size your pump properly. Using your info, in order to get 150k btus out of your heat exchanger with a 20 degree drop you are looking at pumping 15 gpm through your system to accomplish that, this equates to 24 feet of head on your pump. Your pump is capable of pumping only up to 19 feet of head at 0 gpm. So since your pump is not capable of producing such gpm that means that you are going to have larger heat drop or delta t across the heat exchanger in turn sending colder water back to the boiler.

[WoodMOJoe]

If your calcs are correct I guess the worst case is that I may need to get a bigger pump, which I hope to someday install in my nice cozy basement.   

My gas upflow forced-air furnace is 100K BTU, and it heated the house well, so I can't imagine needing to pull the full 150K BTU.  The 19x20 hx was sized to fit my plenum, not because I thought I needed 150K BTU.

At this point I am really just wanting to know how to hook up my underground lines to the furnace, do I need anything besides ball valves, or should I make provisions for anything else at the outside connections?

[hondaracer2oo4]

Sorry, didn't mean to beat you with the calcs, just didn't want to see you undersize your system and be disappointed in performance. You should have a ball valve before and after the pump so that you can isolate it when it needs to be replaced without having to drain the system. I would also think about putting a ball valve with a union  before and after your water to air hx and the dhw hx. That way you can also take those out of the system to do maintenance or replace without making a big mess. Since you don't have your pump outside I would also think about putting a union on either the return line or feed line before it connects to the boiler so that you can disconnect it and blow your lines out with compressed air if you ever have an issue that you need to take the boiler out of service in the winter time to prevent the lines from freezing.

I think you are going to do just fine if your current system is only 100k btu. I live in a 220 year old house in New Hampshire. My oil furnace is 200k btu with a 2 gph nozzle! Its a beast, so I really needed to make sure that I had all of the btus possible.

[WoodMOJoe]

Here's what I came up with for the boiler line connections:



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[Scott7m]

I just brushed up on the heat loss calculations etc. I looked up the 19x20 HX which is rated at 150,000 BTUs. If we plan to get 150,000 BTUs out of it with a 20 degree Delta T this is the calculation for the amount of GPM we need to move to accomplish that.

GPM= BTU/Delta T/500

So GPM= 150,000/20/500 = 15

So in order to extract the 150,000 BTUs from the heat exchanger and get the 20 degree heat drop we are looking for then you will have to flow 15 gpm. So my using the chart found at http://www.pexuniverse.com/pex-tubing-technical-specs we can see that 15 gpm through 100 feet of pex with no fittings will be 11.4. But remember that the GPM that you will flow depends on your pump size plus any restrictions after the pump such as pex length, fittings, heat exchangers etc. So anyways if you could gather the info about pex length, size, fitings, heat exchangers, and pump size we can help you figure it out.

These numbers on coils are about useless, they dont know the temp of the water in our systems, they dont know how many gpm we have, and who knows how hot the water or what the gpm was when the little China man tested it.

Nor dp we know the cfm of the furnace blowing through it??

Its all good to have the math, but experience teaches me to not put much faith in it

[willieG]

furnace fans  can run anywhere from 700 to 2000 cfm and your actual heat extraction also depends on air temps entering the exchanger as well as everything scott mentioned. for a general idea of actual heat needed you might locate a chart that gives average btu ratings per square foot for the area of the country you live in (if you cant get a real heat loss done) and go from there

[hondaracer2oo4]

Here is the chart that I have used in the past. I believe these to be pretty accurate. They seem to be tested numbers and not just something that someone picked out of their head. http://www.heatexchangersonline.com/airtowater.htm

[Scott7m]

Here is the chart that I have used in the past. I believe these to be pretty accurate. They seem to be tested numbers and not just something that someone picked out of their head. http://www.heatexchangersonline.com/airtowater.htm

May be, but who knows what the cfm is of the system they already have is, is it being restrictive due to excessive ducts or other restrictitons. 

There are sooo many variables.....

The only way to know anything for sure is to do a heat loss calculation on the home, then often times were limited by available space in the unit construction.  ive had to put 12x18 hx in homes over 4000 sq ft

[Scott7m]

Here is the chart that I have used in the past. I believe these to be pretty accurate. They seem to be tested numbers and not just something that someone picked out of their head. http://www.heatexchangersonline.com/airtowater.htm

Thats one of the best charts ive seen tho, ive got many resources here from different coil suppliers, same sized coils might show as much as 50kbtu diffefent depending on manufacturer or supplier