Need control design help

Don Baker

I am going to install a new power vent boiler this week to take over for 2 aging oil fired furnaces in a duplex.

The system basics are 1 direct vent gas fired boiler (Burnham series 2pv). This will suppply hot water for 3 zones.

2 zones are going to be heat exchangers mounted in the existing ductwork (1 for each small apartment) and the last zone will be some fin and tube in a previously unheated area.

My biggest concerns are
1) Let the circ pump run 24/7 ?

2)If I used end switches to kick on the fan pushing air through the heat exchanger, how do I let the fan run past the end switch off time. And for how long after the thermostat is satisfied.

A little background; I am an electrician with a bit of boiler experience but no control design. I am thinking I use a couple of expensive timed relays to control the fans off time or is there another device that will handle the fans load?

Or am I out to lunch and need to control the circ pump with the end switches (or something else) and find another way to control the fans.

Thanks for any sound advice
Don Baker

Don Baker

I am going to install a new power vent boiler this week to take over for 2 aging oil fired furnaces in a duplex.

The system basics are 1 direct vent gas fired boiler (Burnham series 2pv). This will suppply hot water for 3 zones.

2 zones are going to be heat exchangers mounted in the existing ductwork (1 for each small apartment) and the last zone will be some fin and tube in a previously unheated area.

My biggest concerns are
1) Let the circ pump run 24/7 ?

2)If I used end switches to kick on the fan pushing air through the heat exchanger, how do I let the fan run past the end switch off time. And for how long after the thermostat is satisfied.

A little background; I am an electrician with a bit of boiler experience but no control design. I am thinking I could use a couple of expensive timed relays to control the fans off time or is there another device that will handle the fans load?

Or am I out to lunch and need to control the circ pump with the end switches (or something else) and find another way to control the fans.

Thanks for any sound advice
Don Baker

Unknown

Don, what kind of air

handlers are you using. If I read you correctly this is going to be two zones with hydro-air (hot water feed to coils in the air handler). Many air handlers have built in controls to operate their blower. These can be set in the handler itself.

The 2 PV uses a control center to bring on the circulator so a constant circulator is not needed. What you may want to look at is Primary/Secondary piping with seperate circulators for each zone. Two for the air handlers and one for your finned tube baseboard zone.

The thermostats for the air handlers bring in each seperate air handler and the air handler then operates the boiler circulator and zone circulators. Just about any of the multi-zone panels out today will work to do this.

If Glenn Stanton from Burnham sees this post I am sure he can give you some exact direction as to how Burnham would advise hooking this up.

Don Baker

Air handlers

Tim;
Thanks! The air handelers are my old furnaces cut down and gutted out, basically I am just using the bottom 1/3 of the old furnaces to house a direct drive fan and heat exchanger. Supply air will be off the old cold air return.

The reason behind this is the apartments are small, this way I can put my homemade air handlers in the crawlspace(where the existing ductwork is) whick completely frees up the old furnace room for future expansion.

Does this make you cringe?

Tim; I beleive it was you who sent me a fax on some old honeywell stats, the drawings showed me where my problem was, thanks I really appreciated you efforts.

Unknown

No I do not cringe

very easily.

What you might think about for control of those old blowers is putting SPDT aquastat controls into the piping at the units. Something like a L6006 would do it. The only other way is to incorporate an Electronic Fan Timer control using time on time off control but then air flow and temperature balance become an issue. You will have to determine temperature rise across each unit and then work to maintain at least 100 degrees + in the supply at all times when the blowers are running, otherwise you will get complaints of cold air. Typical coil temps for air handlers are around 140 degrees into the coil. The other concern is blower speed on the old units. If you do not have the old specs on those you will have to come up with some figures. The formula is:

CFM = BTUHs (Output) divided by 1.08 X change in air temp

Sample problem:

60 degree return temp 130 degree supply temp

120,000 BTUH's output

CFM = 120,000 BTU's divided by 1.08 X (130-60)

CFM = 120,000 divided by 1.08 X 70

CFM = 120,000 Divided by 75.6 = 1587 CFM

What are you using for a coil in these units (air handlers)?

enough to be dangerous

homemade air handler?


how did you make/where did you get the
heat exchanger for the hydronic air handler?

I want to do the same thing at my house.
I have forced air now and want to get a boiler
to heat some floors and use the existing ductwork
to supply supplemental heat and to heat the areas
where I will not be running floor tubing at first
(like the basement slab)

pasquale

Don Baker

As you can read I am definately no expert in this field and I am not sure this route is recomended but....

I live in British Columbia, Canada and there is a local business called Fort Wood sales. They sell and installing freestanding wood fired boilers to replace furnaces for people who have easy access to wood. These units are a small building that supplies water heated by wood then shipped to heat exchangers.

They were willing to size and sell me a heat exchange for less about 50% of what it would have cost me from a wholesaler. The name on the box is Central Boiler.

I couldn't find a web site but remember the owner telling me they were going somewhere in America heartland to pick up my heat exchangers. I can try to find out more particulars when the business opens (it's 5:50 am here now)

Hope this helps
Don

Don Baker

Tim;
Can you supply the manafactures name for the L6006, so I can investigate.

My boss suggested the old furnaces high low limit to control the fan, is this sound asvice in your mind?

I have traded out the old single speed belt drive fans in the old units for 3 speed direct drives and am guessing I should start on the lowest speed?

Thanks
Don

Unknown

Don at this stage of the

game I do not feel comfortable giving any more advice. The L6006 is a Honeywell product. The fact that you did not know that makes me uncomfortable with going any furtner in assisting you with this product. I feel you need to get a professional heating expert involved with your project.

Don Baker

Unfortunatly for

me Tim, we have no pro's. I wanted to hire this out a long time ago. I live in a semi remote area and cannot even get a plumber to do the copper work. It's getting cold and I will forge ahead on my own. It's a sad state of trade affairs here. Thanks for you help so far, I appreaciate it.

I do feel I have enough trade expereince to get me through this project but wanted to nail it down first time instead of having to tinker for a season or 2.

Don