Boiler environment control

dsc3507

I was watching an edition of "This Old House" and I saw the installation of a boiler control to hopefully save energy and I was wondering if it would work or work well with my boiler.  I have a Weil Mclain VHE6 that I installed in about 1990 that is still going strong. When I say I installed I mean I personally installed so I know a lot about it, not that it is that complicated. It is a single zone two pipe radiator system. 



I did a little research and found a Tekmar 256 single stage controller that looks like it would work. I have a number of questions.



Would this type of controller work with my boiler? The boiler has a very low water capacity. I think there is something like 6-8 gallons in the boiler.



If it would work would it be beneficial in cost savings?



Would I leave the circulator run all the time? Mine is the stock Taco that came with the boiler and has been running for 20 years.



Is this model a good choice? Are their others that could also work?



Doug

Steamhead

The 256

wires into the 24-volt burner circuit to stop the burner if the water gets warmer than needed to heat the house at whatever the outside temperature is. The circulator would still run only on a call for heat, unless you choose to have it run constantly.



Outdoor reset controls like this are proven fuel-savers.

dsc3507

Boiler environment control

Ok Thanks.  Yes the connection would be rather simple. The hardest part would be putting a hole through my 20" stone basement wall!!



What I wanted more info on was how well this works in the many different hydronic heating situations. Mine is an old stone home with radiators and the VHE6 boiler. The system rarely goes to boiler cutoff, which is set to somewhere around 180. Typically for a  20 degree day it might average 160.  The house has a very large amount of mass so a big change in outside temperature would not affect the inside for several hours or even as much as a day.



I see warnings about using this in a non condensing boiler because at the lower boiler temps there might be condensation that could shorten the cast iron boiler life. The VHE6 is a cast iron boiler but it also has a condensing stainless steel upper section for heat recovery. I never see and condensation from it though. The basement is very dry in the winter. Typically 30% humidity or lower.



The question is would the lower boiler temps be bad for the boiler. just how low does the minimum go say on a 40 degree day with 72 inside setting?



Doug

Mark Eatherton

EVERY boiler is a condensing boiler....

at SOME point in time :-)



It's not a matter of IF, but more a concern of HOW LONG it condenses. Unless the boiler is being kept in a ready steady state of hotness, it condenses every time you turn it on. THe condensate generated is evaporated so it doesn't come dribbling out of the bottom of the boiler, and generally speaking, it gets above dew point in short order and doesn't cause major problems. With tight tolerance heat exchangers (copper fin tube boilers) over a period of time, there will be enough accumulation of the byproducts of condensation that the heat exchanger will plug up and require removal and cleaning or replacement. With pin style cast iron boilers, like yours, the tolerances are much bigger and the consequences of initial condensing much less.



Typically, massive condensation occurs with return water temperatures of less than 140 degrees F. If you look at the temperature differential when it is really cold outside, you will get an idea of how much delta T your system generates, which will then tell you how low you can go without exposing the boiler to extreme amounts of condensation.



Typically, you might see a 10 degree differential, therefore, you should not turn the boiler much lower than 150 degrees when it is around 60 degrees F outside. You have established that the boiler is capable of delivering good comfort with 160 degree F water at "design" conditions, so that would be your ceiling.



There are so many variables that it would be virtually impossible to determine exactly what your fuel savings would be, but it is safe to say that you can expect a minimum of 10 to 15% reduction in consumption, and it will also help control significant over shoots in inside temperature.



Back in the good ol' days (15 years ago), when we sold a mid range efficiency boiler, at a minimum we would incorporate an out door reset control. Nowadays, the newer high efficiency boilers come with them on board, and we are seeing a minimum reduction of 30% and as high as 50% depending upon numerous variables, there again.



Rotary hammer drills will take care of the rocks between you and the great out doors :-)



ME

dsc3507

Boiler environment control

Ok thanks for the explanation. I finally downloaded the manual and that explains a lot including a setting for a radiator load.



I looked over my VHE6 schematic and there are two ways I can install this. The VHE series has a forced blower exhaust with a 30 sec purge timer. I could have the 256 just shutdown the gas valve leaving the blower running or shutdown the blower which in turn causes the air pressure switch to shutdown the gas valve. This is the way the high limit on the boiler does it. It disconnects the 120v AC to the blower.



Just shutting down the gas valve and leaving the blower running would be wasteful of energy. I would be pumping air from the basement cooling the boiler to the outside. Probably not a good idea.



Shutting down the blower would probably be the way to go. The problem is that involves opening a 120 circuit. I don't think the 256 is spec'ed for high voltage on the boiler control lines. Does anyone know the answer to this? I might have to add a relay.



Doug

dsc3507

Boiler environment control

Looking at the 256 specs it look like it has a rating for HV on the boiler terminals.



Relay                            —    240 V (ac) 5 A 1/6 hp



So that should answer the questions about running the fan. Anyone have any comments on this hookup?? Anyone used this control with a VHE series or similiar?

Mark Eatherton

That will work...

Also, regards the relay, if your blower is running on 120 volts, the ampacity of that relay is 1/2 of what is listed (120V@2.5A). If the blower draws more than that, then yes, you need to place a relay between them.





The interface seems a bit awkward. Do you have access to the boilers wiring diagram? Maybe there is a better place to interface. I don't like breaking into the safety string for conservation efforts, but it may be the only option.



ME

dsc3507

Boiler environment control

I have a call into Tekmar and I will let you know if I get any help there. I am hoping they have tech notes on specific boilers. Big hope but maybe!



Tying into the high limit would not be a safety issue. It would be in series with it so in the event the circuit to the 256  faulted open or shorted it wold not cause the system to be unsafe.



I will scan a copy of the boiler schematic later.



Doug

dsc3507

Boiler environment control

I received an email reply from Tekmar and they said they were not familiar with my boiler and that is should basically work with any boiler of the age of mine - I.E. single stage.



Attached is my boiler schematic. On the right ladder diagram I marked the connections for the 256 -  5/6 are relay contacts for boiler start.  9 is common, 8 is 24 vac, and 7 is connected to 9 when heat is called for.



Is is desirable to stop the blower when the burner is not running. Opening up the limit circuit and stopping the blower results in the air sensor switch shutting down the gas. This is the what would happen if the boiler reached temperature limit - 180 degress or so.  The circulator would continue to run. When the boiler temperature fell to the differential below 180 the boiler would again fire unless the thermostat temperature was reached.



I guess maybe I should try to contact Weil-Mclain and see if they have anything to say about it.



Doug

Mark Eatherton

Good idea...

Let Weil Mc tell you where it is safe to interface.



ME

dsc3507

Boiler environment control

Message sent to Weil-Mclain........

Tim McElwain

Doug do you still have the

White Rodgers Cycle Pilot mercury sensor on your VHE? I believe they came out with a retrofit to replace the mercury sense system a few years back. The kit# was 510-811-218.



The VHE and the HE II are basically the same boiler. It is not designed to be a condensing boiler it does ho0wever use what used to be called a heat reclaimer in what Weil McLain calls a "Flue Collector Hood". The flue gases are pulled from the heat exchanger through a transition connection to the Flue Collector Hood. The transition area has a flap which opens and closes to allow flue gases to pass into the collector hood which is comprised of a couple of copper coils which reclaim some of the heat that would have normally gone up the flue. This is an atmospheric boiler getting its air for combustion from the room.



Here is my concern from having worked on hundreds of these VHE's. Because you might be lowering the temperature leaving the boiler at itmes to 160 dgrees or less. With a 20 degree "Delta T" the return water temp may be too low. The fact of the built in "Flue Connector" offers sufficient  flow resistance to the flue gases to cause condensing in the boiler or thermal shock to the boiler.



My other concern is how do you vent the boiler as there are several options allowed. My concern there is rotting of the flue due to the inability to properly vent the cooler flue gases. Do you have a condensate drip on the flue?