Two zones; is this the answer?

Chuck_36

      Having a two season past history of low boiler temp. (90-120F) on my Burnham 204 NG units (96K in, 70K out)

       It was suggested I have too much radiator water (100gal) for the boiler to handle.

Each apartment is insulated; with new replacement windows and don't need much heat to be comfortable.  Heat loss is estimated at 50KBTU. and 59K BTU respectively.

      The suggestion was to divide each apartment into two zones, each using about half the water.

      I have two identical boilers, one for each apartment. The second floor happened to have shut off valves, so as an experiment, I shut off the supply to about half the system.      

       Sure enough, the boiler temp runs hotter than I have ever seen before now! On a real cold day I have see it as high as 160F.

        Should I proceed to zone each apartment into two?

        Is there any other way to get the boiler to run in a "Normal" temp. range?

        Three bypass styles had no affect. Two circulator trials had no affect.

         I'm ready to take the zone approach. Thoughts please.

KBP&H_3

Possibly a Taco 00-VR

Looking at settting up a Taco 00-VR as injection mix, or a regular injection mix control w/ pump, it will control the return temp to the boiler and circulate the system until the boiler catches up,, ypu can usually limit the return to control condensation, 140* or so , Check out  Taco or call them in Rhode Island, Possibly one way of doing it.

icesailor

What am I missing?

Am I missing something here?

Between the two apartments, there's 109,000 BTU heat loss?

And the building has a boiler with a 70,000 BTU net output?

And the water won't go over 130 degrees?

I'm confused. Will a 70,000 BTU boiler heat a 109,000 BTU space?

What did I miss?

Mike Kusiak_2

Two boilers

There are two 204's, one for each apartment.

Gordan

Curious...

You say three bypass styles had no effect. A properly piped thermostatic bypass would have no choice but to have effect. It just seems like your thermostat is getting satisfied before the high-mass system has a chance to come up to temp. That's not all that surprising. Piping in a thermostatic mixing valve on a bypass would result in the boiler loop being kept at the proper operating temperature regardless of what the rest of the system is doing.

icesailor

An Answer?

Sounds like another over thought, over designed, over installed and costly installation that isn't working.

For want of a set of thermostatic bt-pass valves. If you had bypass valves, you could by-pass the thermostatic mixer and see if the hot water in the boiler went to the emitters.

I've seen 50 year old hydronic systems work as well as the day they were installed. With a few boiler changes thrown in for interest. I haven't seen any 50 year old mixers. They either have been changed or removed.

That's progress.

(Crank the bypass down so it can't bypass and see what happens)

icesailor

Zones: Water

How was the number of 100 gallons in each system come by? That seems like an awful lot of water for a 60,000 BTU system.  1" pipe or tube is more than big enough to feed/run this system and 100' of 1" pipe only holds 4 gallons of water 4" pipe would only be 40 gallons.

Is someone giving you an air reason? A reason pulled out of the air?

Just curious.

Chuck_36

Radiators and mains

       I figure these systems were installed in the 1920"s as gravity w/ coal. First floor system has 2" mains, some 1.5" mains, radiator EDR is 418 sq. ft. Second floor is all 2" mains, EDR is 450 sq. ft.

       My 100 gal est. is based on pumping down each system a few times and watching the clock, knowing (using a gallon bucket) what the pump flow rate is. Impressive amount of water.

       Both current systems were initially installed with a system by-pass which was unworkable. Much too small diameter. Who knows why?

       Plumbed it the right size (1 1/4" iron), used manual Globe valves, and observed the following winter. No significant dif.

       Changed to boiler by-pass, no significant dif.

       Replaced the GF 15-42 with a 15-58 and tried various speeds. No dif.

       My plumber (Not the installer) says "Your boiler is too small". Not welcome news.

        I will look into thermostatic valves for the by-pass but see no reason it should make a dif.

        The water volume can overcome most attempts of this kind, I'm pretty sure.

        I am the homeowner, live on the first floor, rent the second floor.

        All piping is two pipe direct; second flr is 3/4" CI feeds , first flr is some 1" and some 1 1/4" CI feeds. Second floor seems to work better. runs a bit hotter. (5-10F)

        So radiators are mildly warm. As has been true for years, with oil and now NG. I paid less attention then. The oil boilers contained a lot more water.

        Space heating is satisfactory because the house is fairly tight and walls are blown in insulated, windows are new. Storms retained.

        But the boiler is not protected. The system isn't right. That return water can enter at 80F somedays, rarely above 110F. Not a good sign. Something is very wrong or missing.

        When I had oil heat, no by-passes, the heat felt about the same and the systems behaved about the same. (I can hear the thermostat switch on and off.)

        I suspect I need a "Macro" solution; not try this, try that.

        With a Burnham 204 with cold start up, its going nowhere but to hell.

        Two zones for each apartment may be the only answer.

         I see the effect with my eyes. I have thermometers all over these things.

         I keep records, if I am in the basement and the boiler fires up I record data.

         I am genuinely interested in getting this behind me.

Gordan

How could a properly plumbed thermostatic bypass FAIL to raise the boiler return temp?

The system temp is what the system temp is. As long as system loop water at those low temperatures results in adequate heating, you don't have a problem. Those radiators are in no way negatively affected by the low temps, from the longevity point of view.



A thermostatic mixer will mix in as much of the boiler supply water as it needs, and as little of the system return water as it needs, to keep the boiler return at or above the set temperature. There are many ways to plumb things wrong and few ways to do it right. Changing the circulator speed would change the supply temp but shouldn't be expected to change the return temp appreciably, if at all. It really sounds like there are some fundamental misunderstandings at work here.



Here, read this: http://www.pmmag.com/Articles/Column/c4a8f005b30d7010VgnVCM100000f932a8c0____

Gordan

The above article focuses on circulators

But the concepts are the same for a thermostatic mixing valve, though plumbing details differ. The important thing for you to understand is that putting a 3-way mixing valve with the system return as the cold inlet, the bypass from boiler supply as the hot inlet, and the boiler return as the outlet will in no way negatively impact the ability of your boiler to supply as many BTUs as it can to your system. It will just raise the return temp to a safe (for the boiler) level. What you are suggesting - splitting into two "zones" - will not help, because the boiler eventually has to heat both halves of the thermal mass, and as it is heating one half the other half is getting even cooler than it would be. You may be widening the temperature differential, but that will still mean that your boiler will be spending a large portion of its on-cycle in condensing mode.

icesailor

Zones:

I think that what your problem is being caused by a boiler that is too small for the installed radiation. You have two sets of heat emitters. #1 are the radiators in the rooms. The others are all that 3" piping that needs to be insulated. The old timers used to always insulate these pipes with asbestos insulation.

I remember that you said that each floor had its own boiler? Dividing it into zones will just make your zones smaller temporarily. On a cold day, when you need both zones to be on, you will be back where you started, only worse.

If you have valves on the radiators, close a bunch of them off. If the ones that you leave on, get hot, there is your problem. If you find this to be the case, take an infra-red heat loss thermometer gun and start at the boiler. Shoot the pipes that come out of the boiler. Follow along and see what the temperature drop the system has as it gets to the first radiator. That's why they insulate pipes.

Mike Kusiak_2

Boiler and system temperature

Chuck, I think you are confusing the system temperature with the boiler temperature. You mention that the apartments are now insulated with new windows. So now your heat loss is much lower than it was when the system was originally installed. At that time, you probably needed 160F water in the system to heat adequately. Now your heat loss is much lower, so the radiators are effectively oversized and can meet the heat load with 80 to 120 degree water. The room thermostat is doing its job, and is only allowing the water temperature to rise to the point where it satisfies the present heat loss.



Low system temperature is not the problem. The real problem is that you have boilers that cannot run at the temperatures your radiators and heat loss requires. This would be a great application for condensing boilers, as you would be in condensing mode most if not all of the time, and running efficiencies in the 90's.



Since you do not have condensing boilers, you have to run the boilers at a high enough temperature so they do not condense, yet still supply the system with the low temperature water that it requires.



So you need an effective bypass, or other method as Gordan describes to accomplish this. It is not an unusual problem. All low temperature radiant heat systems operate exactly the same way with a non condensing boiler. You just need an effective method to allow the boiler to run at a higher temperature than the radiation.

Chuck_36

My boilers

From the generous cooperation I have received from all, I will go towards a sensor based variable speed circulator in order to increase the entry water temperature to the boiler to eliminate condensation. I will convert both boilers.  I need to get more application info on the installation details from Taco so I can show them and talk with my plumber. A reference given me to an article by John Siegenthaler nailed the problem I have, where excess water in circulation keeps the boiler running cool and likely is condensing.  

Gordan

Consider a thermostatic mixing valve instead

The re-plumbing will likely be a lot less intrusive, and the whole enterprise less expensive. I regret, in a way, posting the above article because I think that, while the schemes described are appropriate in many cases, they might be overkill in yours. If you post a diagram of how your system is currently plumbed, it should be a simple matter to suggest the easiest way to provide boiler protection.



There are things that a sensor-and-controller based mixing device can do that a simple thermostatic mixer can't - such as providing a variable supply temperature to the system based on either outdoor reset or indoor feedback (or both), AND providing boiler protection at the same time - but if you're simply looking for boiler protection and don't care about that other stuff, a thermostatic mixing valve is the ticket.



If you still want a controller-based solution, look at Tekmar's mixing controllers - 356 or 361 for a variable speed circulator or 360 for a mixing valve. They also make (or resell, anyway) mixing valves and actuators to go with the 360.

Gordan

Got your email

I'm posting here so you can get the benefit of others providing their feedback. According to your description, you're currently piped like the picture on the left, only there's no mixing valve and there is a globe valve on the bypass between the supply and the return - that would be called a fixed bypass. The simplified diagram I attached shows the thermostatic mixing valve in relation to the boiler, the system, and the circulator(s). Either of the two options will provide boiler protection. The left one will result in reduced/variable system flow rates but a relatively constant system supply temperature, and would not be appropriate for a series system loop, but might work for a low pressure drop parallel circuit where flow through the radiator branches is well balanced and high delta-T is appropriate. The diagram on the right should work for any single-circulator system that is working currently; here, the mixer doesn't affect the system flow OR the boiler flow, which are constant, but does affect the system supply temperature.

World Plumber

Thermostatic bypass valve

A properly installed Thermostatic bypass valve would fix that. I installed one on a big apartment building where I never saw the temperature above 120 usually 90 to 110. I used the 140 degree one it doesn't allow the system water to flow until the boiler is 140. I also stopped getting complaints that the back of the house was cold.

MC