Taco 702 Outdoor Reset Not Helping???

kevin coppinger_4

outdoor reset you should not be setting back your thermostat....set it at 70 or 68 and forget about it....kpc

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pennron

Taco 702 Outdoor Reset Not Helping???

I just had a Taco Outdoor reset pc-702 and Taco 6 zone relay installed for $1300. They also reduced the size of my gas orifices from .45 to .48 as per Burnham engineer recommendations. I have an oversized Burnham Revolution rv5 in a ranch with a heat loss of about 40,000 btu.

I'm only using the Taco Outdoor Reset 2 days and I know that is not a proper amount of time to be judgemental but preliminary gas usage is the same or possibly more! I can't tell yet because it has gotten a little colder outside.

I have the design outdoor temp set to 8 degrees. When set at zero it took the largest zone 4 hrs to heat from 67 to 71 degrees (it took about 40 min. w/o the taco). I was told that my Honeywell Visionpro 8000 has to acclimate itself to the Taco and it can take a week. I have now upped the outdoor design temp to 8 degrees to get some hotter water thru the supply.

I have 3 zones with an indirect heater as 4th zone priority, using taco 007 circs with slant fin high output multipak 80 baseboard. Should I just give the system time (1 month) to work itself in or does anyone suspect a problem even though it may be too early to determine. Thanks...

ps. taco settings...boil start= 70, outdoor start=70, boil design=190, boil min supply=80 (was told to go that low cause revolution can handle 55 ret. temps), Diff=Ad, wwsd=70

Bob Sweet

Ron

If I read it right your beginning your heating curve with 80* temps to your baseboard if this is the case I would raise my boiler min. to around 130* - 140*.

DEpending on your heat loss and the amount of baseboard you've got, your boiler design temps might be lowered. Outdoor reset works well with basebaord but youve got to supply the basebord with enough heat to begin the convection process and 80* wont do it. Close the gap between boiler design and boiler minimum and the baseboard should respond much better.

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Rob_32

suggestions

Ron, some thoughts from a fellow Revolution owner. (A very happy one, at that.)

Two days is an impossibly short sample interval unless you are in a lab or have a lot of hi-tech equipment monitoring every last inch of the system. Several months, normalized for degree days, would be better.

If you are in the Northeast, the heating loads have been very light so far. Much of your fuel use is probably for DHW production, for which there would be essentially no change between what you were doing and what you have now. The boiler is ramping up for DHW calls no matter what.

The PC-702 is a 2-stage control, which suggests to me that if you've been talking with Burnham and they suggested it instead of a PC-700, then they are using the internal circ as one stage (first, IIRC), and the burner as another (second). A two-stage type control for this boiler is something that I've inquired about as well. It should maximize the efficiency of the boiler to the extent possible.

I have discovered through trial and error, as well as modeling my heat loss and emitter output, that a practical lower limit for my baseboard (equivalent to slantfin fineline30) is 115F supply. Below that there is probably not sufficient temperature differential between the element and the incoming air to establish decent convection. MP80 might be different, but probably not by much. What Bob said above is spot on.

So far, I'm at around 1F/hr temp rise when recovering from very modest (2-3F) overnight setbacks. Seems to me that's pretty reasonable. The goal of course is to minimize the water temp for the outside conditions. Response time should and will be slow. Once your stat gets trained up, it should perform acceptably. I don't know anything about the Vision series, but I did ditch an old Chronotherm because I felt that it was competing with my controls too much for cycle rates and such (tekmar 260 and the boiler controls as well). I went with a simple stat that essentially only knows to call for heat when below target; it doesn't try to control the cycle rate.

You could use your heat loss calcs to see if you really need 190F at design. My house is 30+ yr old and was laid out for 180F water at design, but I'm pretty sure I can do design (5F) with 165F supply or lower (if it ever gets cold, I'll find out). A lower-sloping reset curve would likely improve system efficiency.

I suggest being patient, watching and recording, and see what happens. Good luck.

pennron

suggestion from cc rob and bob sweet

hi:

Thanks for the very interesting and informative advice. Yes I realize that 2 days is not nearly enough time to evaluate. I paid so much denaro for my boiler system, then found out it was oversized, causing more unneeded gas usage expense. Now I pay $1300 for the Taco and orifices. I guess I want to see payback FAST.

Yes you are correct. The tecmar 260 was initially suggested for my Revolution, but Burnham switched gears and said the 2 stage Taco 702 would get the most efficiency out of the Revolution. I believe you are also correct when stating that stage 1 is the internal circ and stage 2 is the burner.

Now I am a novice with this control. I truly do not FULLY understand the settings and what makes what do what. I was told (by burnham) to set the BOILER MIN> to 80 degrees. I think both of you are saying to set that to a higher number. Something like 115 to 130? And the BOILER DESIGN to 180?

From what I've determined so far is if I raise the OUTDOOR DESIGN setting up then the supply water is hotter and the house heats faster (albeit more gas usage). Originally it was set to 0 degrees but it takes too long to heat up the house. I now have it at 8 degrees.

My house has some high cathedrals in the large zone and my large kitchen has a hydronic kick space heater under the sink cabinet. Eventually I would like to install radiant under the entire tile area in the kitchen, dinette and mudroom (all one area 500 sq.ft) and hope that this control will lower my bills to justify more expense.

If you can give me some exact settings for the Taco 702 to MAXIMIZE the efficiency I'd appreciate it. I know I will have to tinker with the settings, but I want the visionPro, which does have a cycle rate setting to normalize. Also not sure what the OUTDOOR AND BOIL START settings should be. They are at 70 right now. Lastly we keep the large zone at 66 overnight, 67 at 9am and 71 at 5pm. If anything we wouldn't mind the 9&5 to be a little warmer (68 and 73). Thanks and happy holidays to all.

Bob Sweet

Ron

by raising the design low temps your adjusting the heating curve to raise its temp based on the outdoor temps giving you hotter water at a warmer design temp.

You'll have to fiddle with the boiler min temp to dial it in. Start with 115* to see how it reacts, I would set the design temp (outdoor) to the coldest estimated temps you will see during the year. If 115* doesn't react the way you like raise the boiler min temp up.

Night time set back from 66 to 72 might be a little much when using the benefits of outdoor reset, I dont use set back but I'm sure some will disagree with me.

Have fun with the control they are easy to adjust and WILL save you money.

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pennron

settings

hi:

Thank you gentlemen for your input. I just changed the settings to the Taco and Visionpro. The Taco is now set to 0 outdoor design and min boiler is now 115. I left max boiler at 190 and the other settings are 70.

With the Visionpro I'm still using a setback (can't help it I've been doing it so long) but will tinker with it and possibly eliminate it as per your advice. I did cut it back. Its now set at 11PM to 9AM @68 degrees 9AM to 5PM @70 then 5PM to 11PM @72 degrees. I just made note of my gas meter reading and will track gas usage closely. thanks again...

pennron

what do the settings mean?

hi:

While I will fiddle with the control I am somewhat in the dark as to what happens when making changes to the Taco's settings. IE: what exactly happens when say you lower the boiler design temp from 190 to 180? How do you know what setting it should be for a particular boiler?

also how about the relationship of raising the min. boil temp from 80 to 115 and at the sametime lowering the outdoor design temp from 10 to zero. What eactly is the correlation between these 3 settings?

I ask this because the Taco instructions do not explain what exactly is happening (or i dont understand them) when you lower this and raise that etc. Thanks...

Rob_32

graphs

What you are fiddling with can best be explained by the figure on the upper right of page 2 of your 702 manual.

You have four basic variables to set. Think of them as x1,y1 and x2,y2

OUTDR start: sets the x1-value (outdoor temp) for the starting value of the reset curve (line) in the figure. 70F is generally used here.

BOIL start: sets the y1-value (supply temp) for lower end of the curve (line) in the figure. 70F is generally ok for high-mass systems, but for your fin-tube, you will probably want to override this with a BOIL MIN setting (see below).

BOIL DESGN: sets the y2-value (supply temp) for the upper end of the curve (line) in the figure. This is the water temperature that is needed to keep the house at your set temperature (typically 68-72F) at "design" conditions.

OUTDR DESGN: sets the x2-value (outdoor temp) for the upper end of the curve (line) in the figure. This is the coldest temperature your location should see in a given winter (more to it than that, but good enough for now).

The "design temp" is a statistically derived temperature based on local weather records at your location. Example: The design temperature for my area is about 5F. At that temperature, my heat loss calculations say I need 165F water to keep the house at 70F. So my BOIL DESGN is set for 165F and my OUTDR DESGN is set for 5F.

Since you have a rather oversized boiler, it's likely that your installer didn't do or didn't pay attention to the heat loss calculation that should be used to size the boiler. With a 40k BTU/hr loss at design conditions, you could have gone smaller (but you already know that). Assuming of course that the heat loss was done right in the first place.

Your outdoor design temperature should be based on local design temps. A convenient list of locations across the couuntry is here at the bottom of the page: http://www.crownboiler.com/educate/heatloss.asp

I suggest that you do your own heat loss calculation. The slantfin software linked at this site is fine for this purpose. Takes a couple hours for a decent first cut.

You can also figure the output of your baseboard in each room and see what water temperature can be used to satisfy the heat loss at different supply and outdoor temperatures. MP80 baseboard output is list here: http://www.slantfin.com/spec-multipak80.html

and if your handy with Excel you can figure up an output curve for lower water temps using the data here:

http://www.slantfin.com/comfin/techpdf/Engineeringdata.pdf

Play with this kind of stuff and you can pretty much determine, in theory, what supply temp you can get away with at design conditions. If you have more fin-tube than needed for design at 180F then you can drop the supply temp. But you should probably work the numbers to provide a starting point rather than fly blind.

But I gather you're looking for a quick fix. Sloppy and potentially wasteful, but here:

As mentioned above, fin-tube baseboard really doesn't do a lot of good at low supply temps. I've found mine works ok down to 115F, then it becomes pretty sluggish. So maybe set yours for 115F and see what happens. Doing this, you basically put a flat spot in the reset curve (line) as shown on page 3. In your situation, this recognizes the lack of useful fin-tube output below whatever supply temp you find is the useful minimum.

Set your OUTDR DESGN to whatever your design outdoor temp should be.

Set your BOIL DESGN to what the heat loss and emitter output results say will get you a warm house at design conditions.

Moving x2 to the left (warmer) on the figure on page 2 will result in a faster rate of temperature rise as outdoor temp falls.

Moving y2 down (cooler) will result in a lower maximum temperature for a given x2 (and decrease the rate of rise as well).

You could mess around with this stuff all winter. Without the heat loss and knowledge of emitter output, however, you'd be flying blind and potentially wasting a bunch of BTUs. I would argue it's more efficient to sit down for a couple hours and figure up your heat loss accurately, the water temp required to match the design heat loss based on the output of your radiation, and plug those numbers in for a season and see how the system does.