Advice needed - Boilers and hot water heat.

[mrsilv04]

I'm dealing with a situation that isn't working quite right, and need some advice on what is needed to correct it.

We have two Weil-McLain hot water boiler units heating a facility. The original system was forced air electric heat (installed in '78). When the cost of electric heat became an issue, the system was "converted" over to hot water heat. This same system also provides air conditioning.

The boilers have been incorporated into the original forced air system. A grid of copper tubing has been built and the boilers circulate hot water through the tubing. The blower fan passes air over the grid, creating hot air, which is used to heat the facility.

Yep... it's a little bit of a kludge.

Still with me?

Here's where the problems begin. The two boilers keep the water hot all the time... even when there's no call for heat. They sit and cycle 24 hours a day... high limit, off... low limit, on.

When the thermostat calls for heat, the blower kicks on, heats the room, and then the blower shuts off. However, the boilers continue to cycle. They're always ready to go. They're also using a lot of extra natural gas, that is being used to heat water when it isn't needed.

What I would like to see, is when the thermostat calls for heat, that it kicks on the boilers, allows them 5 minutes to heat the water (or a temperature sensor that can determine when the water reaches a set temperature), and *then* kick on the blower fan. When the thermostat reaches the set temperature, then it shuts down the fan AND the boilers.

Is it possible to get that five minute delay (or a temperature sensor) worked into the system, instead of having the boilers keeping the water hot all of the time? What would it take to incorporate a fix like this?

 

[JTK]

I'd think you'd need some type of thermostatically controlled gas valve to fire up the boiler per room temp, then an aquastat type temp control to maintain water temp while the gas is lit. That is a funky setup you've got there!

Joel

 

[Gary Allan]

Quote:
The boilers have been incorporated into the original forced air system. A grid of copper tubing has been built and the boilers circulate hot water through the tubing. The blower fan passes air over the grid, creating hot air, which is used to heat the facility.


How many circuits does this have? You describe it as though it's one heating unit in a massive plenum driven by two boilers. If that were the case, just turn off one of the boilers until you're struggling to keep the place warm.

 

[mrsilv04]

Originally Posted By: Gary Allan
Quote:
The boilers have been incorporated into the original forced air system. A grid of copper tubing has been built and the boilers circulate hot water through the tubing. The blower fan passes air over the grid, creating hot air, which is used to heat the facility.


How many circuits does this have? You describe it as though it's one heating unit in a massive plenum driven by two boilers. If that were the case, just turn off one of the boilers until you're struggling to keep the place warm.



Hi Gary-

It's just one circuit/one unit. I've turned one of the boilers off (until really cold weather hits), but then that one unit just works harder to keep the water hot in the entire system. I'm guessing that just running one *might* use somewhat less gas, but it is only a guess.

 

[mrsilv04]

To clarify:

What they did was remove the electric heat element from the furnace, then they fabricated a four layer grid of standard 3/4" copper pipe which is criss-crossed (about 3 foot wide and deep, and about 8 inches high) to fit in that same area. The two boilers circulate hot water through this grid, then the blower passes air through the grid, which heats the air.

It works fine, but I have to find a way to shut down these boilers when there is no call for heat.

I'm the kid of an electrician, so I'm using the HVAC terms to the best of my ability.

 

[mrsilv04]

Originally Posted By: JTK
I'd think you'd need some type of thermostatically controlled gas valve to fire up the boiler per room temp, then an aquastat type temp control to maintain water temp while the gas is lit. That is a funky setup you've got there!

Joel


There are thermostats to maintain the water temperature while the boilers are lit. The problem is that the boilers are on all of the time, and the only thing that cycles them on and off is these thermostats for the water. The water is always somewhere between the upper and lower limits of the temperature setting of the aquastat.

I can see putting a thermostatically controlled gas valve on the boilers, would that same control also be able to control the blower fan as well?

It appears to me that someone was thinking 'outside of the box' when this system was designed.

 

[oilyriser]

Is the room getting too warm sometimes? You basically have a system that puts out a bit of heat all the time, and a lot of heat when the fan starts.

 

[Gary Allan]

Well, you're going to have to maintain the water jackets in the boilers, no matter what. What shouldn't be happening is maintaining the entire gallons of water in the entire system to that temp.

I assume that we've got forced circulation here. The boiler should only be maintaining its own low mass heat. When the remote thermostat calls for heat it should turn on the circulation pump to deliver it. The two are normally independent on multi-loop circuits ..

In your case they may not be wired in the most efficient manner. The pump may come on whenever the boiler itself requires firing to maintain its static set point ..meaning that you're maintaining a much larger mass of water for no good reason.

Edit: What would probably make sense is to have an interlock for the blower that would require a given coil temp before it turned on. That is, boiler cycles to maintain itself. Remote thermostat calls for heat. Circulation pump turns on. Blower waits until coil temp is ..(whatever) before engaging ..stays on after set point is met (circ pump off) until residual energy is scrubbed from the coil.

 

[duaneb9729]

does the blower run all the time or is it turned on with a call for heat or a/c?

if the blower is turned on by the thermostat it would be easy to rewire it, if you took some pictures and pm me i can help you with that.

sincerely
Duane

 

[mrsilv04]

Duane-

The blower is controlled by a wall thermostat, which calls for heat only as it is needed.

However, the boilers have the hot water grid hot and ready to go, all the time.

 

[duaneb9729]

there is a way to wire them to work all together, i have access to weil mclain boiler wiring diagrams and if you share the model numbers with me i can draw you a diagram that will work with your units

 

[duaneb9729]

having information on the air handler would also be helpful

 

[brianl703]

I think the solution to this problem involves a relay or two.

 

[Gary Allan]

That's what I think. Shouldn't be to technologically complicated at all. There's no reason to have the coil heated 24/7 for instantaneous heat ..unless you're willing to run the boiler to heat the plenum needlessly. The circ pump should be tied into the thermostat and not the boiler ..which should work off if it's own.

 

[rjundi]

I had a heat person in my home for a 20 year Well McClain oil boiler having a similar problem after his previous "fix". He turned down the low temp to 100F to keep the boiler from cycling so often but two of my thermostat's were only wired to circulator pumps(zone 2 & 3) only not the boiler itself. The boiler fired on low temp. The main portion of home worked properly(zone 1) firing the boiler by thermostat then turning on circulator pump once to temp.

He stated what I needed was a new controller with smart temp(outside temperature) that kept boiler low point in relation to outside temp (eg off in summer, higher if colder out) and would also fire all three if thermostat's called and control pumps.

He stated ~$400 installed with an extra zone (total of 4) for future expansion.

 

[duaneb9729]

rjundi, you might need a different heating guy and the controller he suggested, i would be suspect that he has the ability to wire that in properly.

my concern comes from his first two trips to your home.

the type of control that can adjust your boilers water temp as well as turn on your zones are very nice controls and can save you some money on operating costs.

Duane

 

[rjundi]

Originally Posted By: duaneb9729
rjundi, you might need a different heating guy and the controller he suggested, i would be suspect that he has the ability to wire that in properly.

my concern comes from his first two trips to your home.


Duane


What he explained is the current controller is one zone. The furnace was retrofitted from the hot water outlet for the home into two separate zones where an addition was added.

 

[tom slick]

from the sounds of it you have a "hydronic" heating system.

are there no bypass valves in the system? usually in this type of system the water circulates all the time but there is a bypass valve that makes the water bypass the coil. When there is a call for heat the bypass switches to allow water to flow into the coil.

 

[duaneb9729]

there would be no need to have a by pass just proper controls

 

[duaneb9729]

was your addition just done? when he installed the pumps did he install back flow preventers, normaly installing pumps instead of zone valves is a more expensive way to go. zone valves would allow for much simpler wiring and less piping normaly.

didnt mean to knock your guy, from what i read it seemed like the job should have been planned better. and i should know that there is often more going on than what is written here.

again my apologies