Dazed & Confused; Pros/Cons Outdoor Temp Reset Controler

T. Traceski

I am meeting with hydronic heating system contractors on replacing an old natural gas boiler with (their recommendations) a Burnham or Weil-McLain conventional (non-condensing), direct-vent boiler. So far so good, until one of the contractors recomends (and prices) the addition of a Tekmar 260 contol to the Burnham. I don't get it, my 2000 sf home in northern VA is heated thru a single zone, monoflow t loop with free standing cast iron radiators and a programable interior thermostat. What will the addition of the Tekmar 260 add by way of greater efficiency to the new boiler in the existing heat distribution system? Any thoughts on if this is a good idea for me in heating my home or just the contractor in selling a new unit. Thxs.

todd s

Tekmar

Your home sounds perfect for the tekmar. Large cast iron systems lend themselves well to reset. Considering that you may have updated the windows,doors,and insulation since the original system was put in, your home may not need as much radiation as it used to. Rather than remove the extra radiators, why not run them at lower temps and save money every day. The radiators will run at a much lower temp and be much more comfortable. The fuel savings will allow the unit to pay for itself in a few years. I always remember this, the less expensive the installation the more expensive the operation.

Boilerpro_3

An opposite opinion

If the contractor sizes the boiler right and you have only one zone, outdoor reset is not very beneficial on a high mass system. It sounds like yours may be a 1950's cast iron radiator system were the mass was considerably less than on earlier gravity systems with real big piping, so reset may have some benefit.
On converted gravity systems were the design water temp is still 180F on the coldest day because of no upgrades to the structure, I have found that the boiler would cycle a little over once per hour with about a 20 minute burn time (typical winter day) and the system temp would go up about 20F. The sheer mass of these old systems absorbs so much heat from the boiler and stores it, that it is self reseting.

I would not use outdoor reset with a setback stat typically, because recovery from setbsck can be very long.

The chief thing I would worry about is if the boiler has protection from low operating temps...only certain models come with this protection built in. Without it, you can have a whole host of problems from the burners and section rotting out to sooting and creation of carbon monoxide. conventional noncondensing design boilers must reach 140F or higher within a few minutes of turning on, otherwise problems begin to ocurr. With the mass of your system and its self reseting ability, you will need this protection.

Boilerpro

Chuckles_2

No, reset would not do much for you if you have noncondensing cast iron boiler. Reset is a very good thing for efficiency and also for comfort---you may have gotten used to it over the years, but the start/stop delivery of extremely hot water leads to a fluctuating room temperature and piping noises. It's just a nasty and primitive way to heat a house, although that's how it is still done all over th US (not in Europe though).

Unfortunately, cast-iron boilers need the very hot water: return temperatures under ~140F will cause the heat exchanger to deterioriate. There are ways to send cooler water into the radiation while sill keeping the return water to the boiler hot, but if mixing valves (expensive) are not being used, the Tekmar can only vary the water temp between 140 and 180, and that is not a very wide range. With a condensing boiler you can have the water temp vary between 180 and 70 (room temp) which is what is needed.

Bill Nye

Not all about efficiency

It is about comfort! It is like cruise control for your house. Instead of on/off with your t-stat, it is constant luxurious warmth. The heat is replaced as you need it not a big dose of 180° water followed by turning the pump off and letting the radiators cool to room temp and repeat ......... etc.

Constant circ at a lower water temp will make you comfortable. Visit someone that has it in their home. If you don't know anyone you can look me up. I lived in my home over 17 yrs. Only the last 4 have been with outdoor reset and constant circ. You can feel the difference

Constantin

Considering the Cost...

...I would always go with outdoor reset. I'm a mere homeowner, but we got to chew throught his topic some months ago. IIRC, Honeywell had a study showing 16-26% fuel savings using identical homes & heating setups. Tekmar also has some literature.

Anyway, as other have mentioned, outdoor reset is about comfort... the house will maintain at one temperature, hopefully regardless of changes in insolation, exterior temperature, etc. Outdoor reset + constant circulation becomes all the more valuable as houses are buttoned up and the extant radiators become oversized.

The only houses where outdoor reset makes less sense to me are homes with steam heat (though there is perhaps a small marginal benefit) because you cannot modulate the temp of non-pressurized steam down the way you can with hot water circulation.

DaveGateway

A 260 only costs around $300

So why not even if the reset savings are small? Don't forget the other 260 options you could benefit from with an indirect HWH: priority, so a larger output boiler is not needed, and post purge: pump those BTU's after a heat cycle into the indirect rather then allowing the boiler to sit and have the heat lost up the chimney.

David_5

Good idea

It is a good idea to use reset in your situation. It is true a non condensing boiler cannot be run below 140. To do this on the cheap just set the reset so the minimum boiler temp is 140. For a little more money a mixing valve can be added to protect the boiler and let the system temp run lower. I believe these controls save money but it is hard to prove. They definately improve comfort. If you use setback thermostats and reset the boiler temp then use thermostats that automatically compensate the start time.

David

Constantin

That's my point...

... an investment of a couple of hundred bucks is probably made up by year 2 in most homes. Afterwards, you enjoy the tax free benefits (+ comfort!) as long as you own the home. Seems like a no-brainer to me...

hydronicsmike

Outdoor Reset

Should be in any Space Heating Application, regardless of whos Controls you are using. Sounds like a no brainer, but I am still amused every time when I read about some claims that one should not do Reset with Non-Condensing Boilers.

jerry scharf_2

Outdoor reset is a control strategy

TTT,

I think you got some good answers here, and wanted to back up a bit to put it into perspective. Every heating system has a control strategy to keep the living space livable and the boiler burning when you need it. Each one has it's costs and benefits.

The system you have is by far the least complex control system, it has one on/off control for the whole house, one temperature point for the hot water supplied and one flow rate for all the devices to use. It provides the least comfort and the least efficiency, but it is one everyone can understand. It will have relatively wide swings in the indoor temperature caused by a control situation called overshoot. The slower the rate of heat loss in the room, the more the overshoot. Room to room heating differences are usually handled by the "double hung" auxilary control (opening the window.)

Outdoor reset is a control strategy where you attempt to match the supplied water temperature to the expected demand. The demand is assumed to be related to the outdoor temperaure and that temperature is used to set the supply temperature. Though it may at first look like this is for a modulating and condensing boiler, the control strategy can be used with any system with improvements in both comfort and efficiency. If your radiator is getting cooler supply water most of the time, the overshoot and the comfort will be improved. there have been documented improvements with "standard" boilers using the control strategy over the basic thermostat/single temperature. One down side to this is that night-time set back is harder to do. Since you have lower water temperature going to the radiators, it takes longer to recover from the setback. On the other hand, the setback efficiency gain is usually less than the outdoor reset gain.

The next level of comfort and efficiency gain, IMO, is to add room by room control for the temeprature to the outdoor reset. Opening the windows is a huge energy loss that is never factored into the energy efficiency claculations. Adding thermostatic radiator valves to each radiator allows each room to set it's temperature and take just the heat it needs. With this you go to constant circulating water, the boiler runs as necessary to keep the water at that right temperatature. There are no fancy controls to program, and the comfort level acchieved is a marvel to those who have never experienced it before.

Beyond the outdoor reset control strategy, the tecmar unit in question also has other benefits that it brings to the table to increase efficeincy and comfort.

The biggest downside to the tecmar control is that not everyone can understand it. It's something that needs to be "dialed in" for eash system. If you have someone who is familiar with it, talk to their references that also have the tecmar controller. Are those people happy with the system in terms of efficeincy and comfort? Did the installer get the system working well? How did they handle the adjustments to the controls? Buy Dan's book on pumping away and read around this site, then see if the installers are up on how to do near boiler piping well. This is true for every system, but it becomes more appearent as the complexity of the system increases.

best of luck,
jerry

heatboy

How about.......

a two stage thermostat instead of outdoor reset. 1st stage operates the pump and the second stage starts the burner. Wonderfully simple and fuel efficient.

hb

Constantin

Nicely said!

Jerry, that was a great introduction for homeowners to read. Perhaps one day folks will get used to non "bang-bang" control mechanisms. In the meantime, I hope the more educated like you will enlighten the rest of us. Cheers!

ScottMP

BoilerPro

I had a system just like you decribed, old gravity system with a 1960's GE downdraft.

They must have forgot to install the self reseting part that you described.

My house would over shoot the temperature on the thermostat everytime. Old cast iron rads hold Alot of heat. Throw some heat on them, especially 180°, and they will put out heat LONG after the room set point has been reached. SO we get over shooting. Now the room is two to three degres over where its supposed to be ... so we cool down. SO does the boiler, rads and piping. By the time the thermostat kicks in the water temperature in those big old rads is closed to room temp. Circulator comes on and sends a big old slug of 70 degree water back to the boiler, meanwhile the room temp is dropping. And the boiler starts chugging.

Can you say wide swings ? I knew you could.

I did'nt see any reseting going on.

I installed a Buderus boiler with a 2107 reset control with a four way mixing valve and have a very comfortable house.

Ya I know, I threw a four way valve in there but I wanted to honest. I also have seen my water temp going out at 140. Water temp. that more closey matches the demand will give less over shoot.

180 vs 140 hmmmmmm

Savings vs no savings ??

Scott