Central OWB hooked up to Pressurized Benjamin CC500 problems

[Kawliga]

So, I went to the sticky here and used the TACO calculator to see if I can figure out my head and flow requirements so I can pic an appropriate circulator pump....

My total heat load requirements are 100Kbtu/hr., and my ideal delta T is 20 degrees. Thus my target flow rate should be 10gpm.

If I then proceed to size the pipe....I should have had 1.25 dia pex in my lines, but unfortunately...I have the 1" diameter...

I will stick with target flow of 10gpm.

The total length of my system is 310 linear feet.

Using this formula: HL = k x c x L x (f1.75) to determine my head...(I am ignoring any static head from the 70 foot vertical elevation of the OWB and mech room, OWB is above Mech room)
k= 0.00223 (1" pex) tubing size
c= 0.933, (180 degrees, water)
L= 310 ft
(f1.75) = 56.234...which is value for 10GPM....(i might be using wrong value here as the 1" pex can only flow 7.5gpm at 4ft/sec)

The result is 33 feet head.

Based upon the sizing chart, a Taco 0013 or equivalent should be the pump of choice....is this a reasonable assumption?

I did not factor the head for the flow passing thru the DHW HX and Boiler HX....(I dont know what the facotr here is)...is that a big problem?

Does my math make sense?

Mike

 

[lkdiver]

Couple of random thoughts:

- Using high-head circulators in opened systems has it's own set of problems - there is Net Positive Suction Head (NPSH) specification for the pump. Do a search - for high head circulators the required head is high enough that it is difficult to achieve in an opened system (since you have 70 ft of static head, you indeed may be better off with pump in the mech room)

- There is nothing magical about delta T of 20 degrees. If you accept delta T 40 degrees, your flow drops to 5 gal/min... Much more manageable with 1 in PEX.

- Adding mixing valve in the mech room will add additional flow restriction (possibly significant based on what valve is used).

It I was doing this (and this only my opinion) I would:

1. Leave the pump alone for now, correct obvious plumbing deficiencies - reconfigure to series hookup with counter flow configuration (I guess we could flip a coin if DHW should be first or the house - but if you have plenty of hot water now and not enough heat in the house I would certainly attempt to maximize house performance)

2. If return temperatures are too low, I would add bypass pump at OWB (discussed here many times - small pump between OWB outlet and inlet to raise return temperatures by mixing)

3. You may want an aquastat to kill the supply pump if the outlet temperature at OWB is too low (OWB not keeping up with the load or out of wood).

 

[bigburner]

Your numbers look about right. I use two taco 011 push/pull on 250' of pex and another 125' of inch copper & one very large HX, rest is primary /secondary My point here is I have a measured 6 gpm. I heat 2500sq house - water to air Hx + in floor + DHW + 1000 sq ft pool room and 12,000 gals of water and do it with 140F water most of the time. + my garage at 50F, my splits run about 25 on the Water to Air when furnace fan is running - I continuous feed the DHW tank - which operates the in-floor. The pool will pull out 12F when running [only at night]

Ok - here is my newest idea, get ride of the HX for wood boiler, you have plenty of TDH from the fact that the boiler sits on a mountain - Just run it open system that takes out one complete Heat exchange which might cost you 10 degrees. With all the pex on the pressure side you should be using treatment in the water anyway. This is what I might do, HX work the best when you have a large Heat differential - example if the boiler was running 212 degree water and you biggest load would work with 140 degree water that gives you way more BTUs to work with. 'Just more opinions"

 

[Kawliga]

Your numbers look about right. I use two taco 011 push/pull on 250' of pex and another 125' of inch copper & one very large HX, rest is primary /secondary My point here is I have a measured 6 gpm. I heat 2500sq house - water to air Hx + in floor + DHW + 1000 sq ft pool room and 12,000 gals of water and do it with 140F water most of the time. + my garage at 50F, my splits run about 25 on the Water to Air when furnace fan is running - I continuous feed the DHW tank - which operates the in-floor. The pool will pull out 12F when running [only at night]

Ok - here is my newest idea, get ride of the HX for wood boiler, you have plenty of TDH from the fact that the boiler sits on a mountain - Just run it open system that takes out one complete Heat exchange which might cost you 10 degrees. With all the pex on the pressure side you should be using treatment in the water anyway. This is what I might do, HX work the best when you have a large Heat differential - example if the boiler was running 212 degree water and you biggest load would work with 140 degree water that gives you way more BTUs to work with. 'Just more opinions"

Ahh, you're killing me big burner...lol. I did mention that in a previous post in this thread, to tie direct to my indoor loop and omit the boiler HX....however that will only be my last straw resort...If I tie in direct, I have no backup boiler, and no backup heat system...in addition my indoor loop is a 50/50 glycol mix...and I dont want to fill the CB with 100 gallons of glycol...too much dinero. If I could get some bucks for my benjamin boiler and oil tank, I would reconsider, then I could throw in a fe electric baseboards....

I really want to have my existing oil burner on line for backup....just for when we go away.

For the time being I have shut down the loop to the DHW HX from the manifold and I am getting 125F water in my indoor loop so we are having plenty of heat. I'm waiting to go into town and pic up some cheap thermometers to take readings on all 4 pipes on the boiler HX just to see what is happening...

Good advice Lk diver too....

Keep ya'll posted and thanks for the opinions...

Mike

 

[bigburner]

My last idea won't work" open system", unless your boiler is rated for 50 PSI because you'll have 30 psi before you start. If it is rated for 50 PSI just change the blow off, the rest of the components should be rated for the pressure.

another idea is to isolate the gas boiler with the HX and run the rest of the house on an open system, You can get some great Delta T when operating the gas boiler and no HX loss on wood. You have unique situation where this will operate like a closed system other then some evaporation & water treatment. There is a system wood chip boiler near me that uses a 200,000 gallon storage tank, same deal. the tank is 40 ft tall no need to pressurize.

please post a picture of the OWB setting on the mountain, do u use a ladder to get to it. LOL sorry couldn't help my self.

 

[Countryboy1966]

Kawliga,

Just wanted to give you an update on my issue. Changed the 1/12th HP B&G Series 100 to a Taco 0013. I did not get the results I was expecting. Although it was midnight last night and I did not do the best monitoring job, I was only able to get the process water up to 140°.

Next I am going to plumb the pump into the house near the HX and then put my B&G 100 back in at the OWB. I will let you know what I find.