Burnham Revolution & Taco 702 ODR

pennron

Glenn:

The L8148e is set at 200 per Ron Beck's instructions. I know its supposed to be 210. Ron suggested that setting and also had my orifices reduced from .45 to .48. Ron figured a combination of all these changes would help significantly. I have definitely saved on fuel but I can't seem to nail down the Taco settings. It just takes so long to reach my stats settings and like yesterday the stat never reached 74.

I'm looking for ideal settings in mild and cold weather with the most fuel efficiency as possible. I don't know if thats possible w/o changing settings during mild to cold weather. I also don't know if when changing the taco settings if the control needs an amt. of time to adjust to them (a day, week?) because its based on a ratio or curve.

The sensor is located on the supply pipe. I have included a pic. The sensor is located exactly midway between the expansion tank and the elbow (the elbow that turns toward the expansion tank) on the top of the supply pipe, with insulation tie strapped around it. The outdoor unit is on the north side well hidden from the sun and wet weather. The temp. reading is accurate, maybe a 1-2 degree difference from the actual outside temp.

Hope this helps. Also to my question earlier. Is the boiler supply temp supposed to be lower than the boiler target temp? Any other ideas or suggestions greatly appreciated. Thanks...

pennron

Burnham Revolution & Taco 702

hi:

I have a Burnham Revolution RV5 (oversized, should have rv4) and Taco 702 ODR. Burnham tech. suggested using the 2 stage taco and having it wired with the 1st stage operating the internal revolution circulator and stage 2 firing the burners. I find that with the settings I'm using that my 2400ft well insulated ranch doesnt reach temps especially in milder weather. I am trying to balance keeping my house warm and using as little cubic ft as possible (well who isn't right?)

I have been using design & outdr starts of 70, boiler design of 165 and outdr design of 0. I have changed those numbers to be 73,73,175,9 respectively. while this has raised the boiler target temp a few degrees my stat still can't reach the 74 we desire.

Right now the taco at 54 degrees outside has a 103 boiler target, but the boiler supply temp on the taco is 89. How can the supply temp be 14 degrees below the target? does this indicate a problem? I would think the boiler should maintain a temp. closer to the target, correct?

my boiler min. setting is at 80. burnham said to use that setting because the revolution can handle 55 degree return temps...I am using slant fin multipak high output fin baseboard. any help on the settings is appreciated.

Unknown

Ron

What temperature is the high limit of the boiler's L8148E set at and where is your 702's system Supply Sensor located? One or both of these may be the problem.

Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.

scott markle_2

design temp.

Ron, if your desired indoor temp is 74 then this should be your design temp setting. Are you doing any night time setback? if so your curve will need to be a bit higher if you want reasonable recovery. The closer you have your curve matched to actual loads the more efficient your system will be. But this comes with a performance trade off in that the low water temps will be slow in making upward adjustments to room temp. A well insulated house that does not have an especially high solar gain can actually be well regulated by outdoor reset alone. If you want your room thermostats to function responsively like in a conventional 180 deg. system you will need to operate at a higher curve.

There are control systems that utilize a combination of indoor and outdoor information to regulate temperature and cycle length such that zones with different demands can operate predictively at water temps required by the zone with the highest load. Lets say you want the bath zone to be especially warm, the control recognizes the large discrepancy between actual and desired room temp and supplies full 180 water to expedite this request. in-order to preemptively avoid overheating the other zones these zones are put into a on/off cycle based on the discrepancy of the higher temperature and the individual needs of these zones. Tekmar tn4

As far as your system is concerned I would focus less on what the thermostat says and more on how you feel. There is a lot of anecdotal evidence that people are comforted as much by a perception of control as by actual environmental conditions. One aspect of well tuned outdoor reset control is that the sine wave fluctuations that are the inevitable result of conventional indoor thermostatic regulation are largely eliminated. Also the lower water temps and near constant circulation that result from ODR provide a higher ratio of radiant to convective heating. It is believed that the even nature of this heat delivery can provide comfort at lower over all room temps.

Not to be judgmental but given the nature of our energy future 74 seems a bit high to me. Perhaps the idea that you require this degree of comfort needs adjustment more than your reset curve.

The discrepancy between boiler supply temp and target temp may be nothing more than differential temperature. A wide differential is often required especial if the equipment is oversized to avoid short cycling.

Unknown

Ron

I would increase the Boiler Start Temperature in 5°F increments on milder days until you get it to where you feel comfortable. This also happens to be Taco's advice per their manual.

"Boiler Starting Temperature (BOIL Start)"

"The BOIL Start setting is the starting supply water temperature of the reset ratio, and can be adjusted from 35 to 150°F (2 to 66°C). This setting is typically set to the desired building temperature. In applications where fan coils are used, the BOIL Start may need to be set higher to prevent cold drafts during mild outdoor conditions. If the building feels cool during mild outdoor conditions, the BOIL Start setting should be increased."

Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.