Someone please double check my calculations?

General Outdoor Boiler Discussion
larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Someone please double check my calculations?

Post by larryjbjr » Tue Jul 04, 2017 1:08 pm

Ok, I really appreciate all the help I've already received on this forum. This is my first OWB installation, so still have a lot of questions.

Right now I'm working on hooking up the plumbing.

My OWB is located 75 feet from my house. Then, once it gets in the basement it is about another 30 feet to the existing LP boiler. I'm planning to put the flat plate heat exchanger on the return side of my LP boiler. As best I understand that is best. But, that is another question altogether.

Anyway, it is 75 feet to the house, then another 30 feet to the heat exchanger. So, 105 feet each way gives me 210 feet of 1" pex. I don't expect to have any elbows or T's or anything of the sort until I get to the heat exchanger. There I will probably have to put in two elbows on the supply and return, so a total of 4 elbows.

Now, based upon the typical head loss calculation, I've been told to multiply my total pipe length, 210', times 1.5 to account for T's and such, then multiply that times .04 to get head loss. So, 210X1.5=315 315X.04=12.6 So that would give me 12.6' of head loss.

The question I have is, since I have no T's and only 4 elbows, will my head loss really be that high?

I'm planning to use a Bell and Gossett NRF-22 pump, and at 12.6' of head loss I would only have about 5GPM flow.

Right now I'm planning to run two 1" pipes to the house. One to feed the LP boiler and heat the 2000 sf of living area. The other to heat the DHW and also to heat the approx 1000 sf basement.

Bull
Posts: 56
Joined: Sat Oct 29, 2016 9:18 pm
OWB brand: Central Boiler
OWB Model: 4436
Location: Southern Indiana

Re: Someone please double check my calculations?

Post by Bull » Wed Jul 05, 2017 5:08 am

What are you going to heat the basement with? I think you can do this with 1 set of lines but RSI is the pro so we will see what he thinks.

larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Re: Someone please double check my calculations?

Post by larryjbjr » Wed Jul 05, 2017 10:32 am

Cast iron radiators in the basement. Plan to continually circulate water thru them.


Sent from my iPhone using Tapatalk Pro

RSI
Posts: 308
Joined: Mon Jun 23, 2014 8:51 am
OWB brand: HeatMaster
OWB Model: G200
Location: South central Wisconsin
Contact:

Re: Someone please double check my calculations?

Post by RSI » Wed Jul 05, 2017 11:58 pm

Head pressure is completely dependent on the flow rate. If you increase flow, head goes up and if you decrease flow it goes down.
If I have time tomorrow, I will see if I can calculate an estimate on what it would be.

Is this a newer house or older with poor insulation?

Do you already have that pump or is it something you plan on purchasing?

larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Re: Someone please double check my calculations?

Post by larryjbjr » Thu Jul 06, 2017 5:14 am

It's an old farmhouse but I insulated it fairly decent a couple years ago.
I already bought the pump. I could possibly return it though.



Sent from my iPhone using Tapatalk Pro

larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Someone please double check my calculations?

Post by larryjbjr » Thu Jul 06, 2017 5:14 am

---

RSI
Posts: 308
Joined: Mon Jun 23, 2014 8:51 am
OWB brand: HeatMaster
OWB Model: G200
Location: South central Wisconsin
Contact:

Re: Someone please double check my calculations?

Post by RSI » Thu Jul 06, 2017 11:22 pm

You will not want to have always circulating through cast iron radiators.

What I would do it put the plate heat exchanger on a primary loop and the radiators and forced air heat exchanger on a secondary loop. The pump you have would be good for the secondary loop and depending on what is in the primary, something like a Grundfos 15-58 or an ECM pump would probably work fine.

I would set it up so the secondary loop pump came on with the furnace blower. You could add another thermostat to turn just the pump on or have a manual switch for it if you want more continuous heat out of the radiators during the colder part of the winter.

larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Re: Someone please double check my calculations?

Post by larryjbjr » Fri Jul 07, 2017 12:41 pm

RSI wrote:You will not want to have always circulating through cast iron radiators.

What I would do it put the plate heat exchanger on a primary loop and the radiators and forced air heat exchanger on a secondary loop. The pump you have would be good for the secondary loop and depending on what is in the primary, something like a Grundfos 15-58 or an ECM pump would probably work fine.

I would set it up so the secondary loop pump came on with the furnace blower. You could add another thermostat to turn just the pump on or have a manual switch for it if you want more continuous heat out of the radiators during the colder part of the winter.
I think there may be a little bit of confusion here.

I do not have a forced air heat exchanger, only planning to use plate heat exchangers.

If I understand you right, I should use a 15-58 pump on my primary loop, which would be the heat exchanger feeding the propane boiler. Now that boiler feeds the radiators and such that heat the ground floor and second floor of the house.

Then you're saying I should put the bell and Gossett pump on a secondary loop to feed the two plate heat exchangers that heat the DHW and also heat the basement, via cast-iron radiators. And that I should have the secondary loop kick on whenever the furnace kicks on?

Just wondering, why would I not want constant circulation through the radiators in the basement? Seems like it would be the best way to go without having to hook up a thermostat and pump controller and whatever.

RSI
Posts: 308
Joined: Mon Jun 23, 2014 8:51 am
OWB brand: HeatMaster
OWB Model: G200
Location: South central Wisconsin
Contact:

Re: Someone please double check my calculations?

Post by RSI » Fri Jul 07, 2017 6:42 pm

Unless the radiators are really small, it will get way too hot in the basement when the weather isn't as cold.

You want the water always circulating through the DHW plate exchanger.

I didn't realize you have a boiler in the house instead of forced air. You will probably want to just put the two plate enchangers in series. Do you have radiators in the whole house? If so, how well do they heat it? Does it ever have trouble keeping up? If so, you may want to go with 1-1/4" pipe and or larger pump to get higher flow rate and keep the delta T to a minimum.

There are a lot of different ways you can tie into the existing system. One common way is to use a wrap around pump that just circulates water through the indoor boiler and plate. If you do that, the B&G pump you have would be good for that.

larryjbjr
Posts: 34
Joined: Mon Jun 12, 2017 7:17 pm
OWB brand: Johnson
OWB Model: Little John
Location: A bit north of Milwaukee WI

Re: Someone please double check my calculations?

Post by larryjbjr » Fri Jul 07, 2017 6:59 pm

It would be two radiators about 6000 BTUs each. Would be around 10,000 BTUs or so per hour. It would really be just enough to heat the basement that's about it.




Sent from my iPhone using Tapatalk Pro

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests

cron