Choosing an outdoor reset


  #1  
Old 12-09-13, 08:40 AM
T
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 65
Upvotes: 0
Received 0 Upvotes on 0 Posts
Choosing an outdoor reset

We have a two zone Burnham ESC4 controlled by a Taco SR504EXP box. Would like to add an outdoor reset to control the Slant Fin baseboard heater water temperature.

Burnham makes one (IQ 102723-01) which plugs into the boiler. I've also been looking at a Taco PC-700 which plugs into the Taco SR box. The benefit of the Taco is that is adds warm weather shutdown, which is something we'd like to have and we are leaning towards that model. It also has a price advantage.

Some questions:

1) Would it be beneficial to have an ODR that also looks at the indoor temperature?

2) Is there another model that's preferable to the two I listed for basic ODR control for a modern non-condensing cast iron boiler?
 
  #2  
Old 12-09-13, 04:14 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
Before we talk about choices, let's first learn what your expectation of savings is, and a little bit about how your boiler behaves in real life.

Do you have a savings expectation? How much? Have you weighed the possible savings against the cost of the ODR units to arrive at an expected payback period?

How good is your knowledge of the boiler water temperature now? i.e.

Does the water temperature consistently run above say 150F?

Has the boiler been installed long enough to have observed the behavior on the COLDEST days of winter and do you know what the water temperature was then?
 
  #3  
Old 12-09-13, 04:35 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: United States
Posts: 2,681
Upvotes: 0
Received 59 Upvotes on 49 Posts
Two important questions , 1-do you have an indirect water heater? 2-how many heating zones?
These answers could make a difference. The savings and water temperature depends on heat loss and amount of radiation.
You won't know the water temp required without the heat loss. Where the water temp goes on the boiler as it is operating now really does not tell us much. If the boiler is zoned the temp will hit limit just due to that fact.
 

Last edited by NJT; 12-09-13 at 04:51 PM.
  #4  
Old 12-09-13, 04:57 PM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
Outdoor reset control

A fact that is good to consider when heating with water is, for every three degrees that the water temperature is lowered there is a 3% fuel savings and this savings is not depended on any one temperature it is always the same. The room temperature unit RTU automatically set the target temperature. If the room goes above its setting it automatically selects a new point on the heating curve, without it you will have to turn the thermostats at their highest and let the room temperature go above a comfortable temperature and manually adjust a new heating curve . So unless you have a lot of time or just like to experiment a RTU. is the way to go . I like the Tekmar units as they are very user friendly and have WWS . Hope this gives you food for thought.
 
  #5  
Old 12-09-13, 05:29 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
for every three degrees that the water temperature is lowered there is a 3% fuel savings
I think that's pretty optimistic IMHO.

Did you mean for every THREE degrees, ONE percent of fuel savings? Still overly optimistic. Where did you learn that? Would you cite your source please, I would like to read the report and decide for myself.

You aren't talking about THERMOSTAT setback are you? That's one place that I've seen those numbers quoted... every 3 degrees of thermostat setback is supposedly equal to 1% of fuel savings.
 
  #6  
Old 12-09-13, 05:41 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
The room temperature unit RTU automatically set the target temperature. If the room goes above its setting it automatically selects a new point on the heating curve, without it you will have to turn the thermostats at their highest and let the room temperature go above a comfortable temperature and manually adjust a new heating curve . So unless you have a lot of time or just like to experiment a RTU. is the way to go
This part of the discussion does not apply to either of the ODR that OldGuy is asking about, just so that there's no confusion here.

ODR does not require a lot of experimentation to set up.

You set your BOILER MAX, BOILER MIN, and a few various temperatures, and you're done. It is that simple.
 
  #7  
Old 12-09-13, 06:26 PM
T
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 65
Upvotes: 0
Received 0 Upvotes on 0 Posts
To answer some questions:

It's a two zone system, but we might be better off using it as one. Each zone is about 75' (+/- 150' total) with contractor grade Slant Fin baseboard running 100% along the exterior walls. It seems that when one thermostat turns off the other turns on. That seems detrimental as both zones are sometimes kept at the same temp and the boiler cycles more than it needs to. OTOH, there are times when the second zone isn't even on or can be set considerably lower than zone one. I don't know what a happy medium is to maximize efficiency between zones.

There is a separate hot water heater, totally independent of the boiler. The 1882 home is cellulose insulated with high ceilings, large rooms and some massive old windows with weights - with cold floors from a cold basement (insulating the perimeter joist bays helped but insulating under the floors was futile) so the heating system carries a load. The system in question supplies only the first floor, there is a second steam radiator heating system in the home for the other floors, a design which goes back way before we bought the place.

The major incentive in getting an ODR is a $250 use it or lose it credit that expires at years end. The concept makes it sound like a good thing to have, regardless of the incentive.

So which ODR should I go with, and is it beneficial to have one that also looks at indoor temperature?
 

Last edited by thatoldguy; 12-09-13 at 07:00 PM.
  #8  
Old 12-09-13, 08:59 PM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
Outdoor reset control

Sorry for the 3% I did mean to say for every 3 degrees reduction in water temperature there is a 1% fuel savings that is why the powers at be are probable offering the incentive to install. I will try and be more carful in the future .
 
  #9  
Old 12-09-13, 10:04 PM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
Outdoor reset control

Thatoldguys first Question was, should I purchase an ODR control that also looks at the indoor temperature? I took that to mean a RTU. N.J.Trooper to answer your question on where I came up with 3 to 1 was in a Canadian heating,plumbing, and air conditioning magazine HPAC in an article written by John Siegenthaler,P.E.author of Modern Hydronic Heating . The title of the article was I believe onward and downward , where he talks about how in the past with cheap fuel a design temperature was set at 180f and now it is time to put in more heat emitters that will delivers the same btu with 120f water temperature .The article was written as a result of my email to him as to why 180f is still being used when we know there is a 30 to 40 % fuel savings by using outdoor reset . An example of this is my 4 apartment home , with an outside temperature right now of 23 degree f is being heated with 86f water in slant fin baseboard heaters. Hope this sheds some light on why to use ODR.
 
  #10  
Old 12-09-13, 10:21 PM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
NJ Trooper I spent this afternoon with a tec. rep. working for Buderus boilers and the question came up as to how you fine tune an ODR to deliver the optimum water temperature , his answer was a RTU or turn up the thermostats above your comfort level and then play with the control until the room maintains a temperature a few degrees above your comfort level and then use the thermostat to fine tune the actual room temperature desired. I have done this and I prefer a RTU to do it for me.
 
  #11  
Old 12-10-13, 04:40 AM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
Outdoor reset control

N.J Trooper more on where I came up with the low water temperatures , in the may june 2012 HPAC magazine on page 34, John Siegenthaler,P.E.in his article Selective Coverage under the heading Watch The water Temperatures he writes. The thermal efficiency of condensing boilers is dependent on the water temperatureat which the heat distribution system operates. The lower the better.He proberly would agree a more precise statement would be that the thermal efficiency of condensing boilers depends on the water temperature returning to the boiler. Hope this helps you understand what ODR is all about.
 
  #12  
Old 12-10-13, 05:31 AM
T
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 65
Upvotes: 0
Received 0 Upvotes on 0 Posts
Interesting reading but...

I had to google what a RTU is, and also found the article you're mentioning here:

Selective Coverage

To keep this on track, it was posted that this is a contractor grade Slant Fin baseboard heating system. The article refers to radiant panels which I assume have different design temps, especially since you also mentioned an operating temp of 86F on a 23F day. I'd expect Slant Fins to be warm to the touch but not convect or radiate any significant heat at that temperature. It's also posted we have a conventional cast iron boiler, not condensing. It appears the articles(s) are geared towards modern, energy saving design with high tech means which is not present in this situation.

Is what you write of applicable to the ODR we'd like to install, or posted as useful information for NJT and others working with the leading edge?

From what you wrote, should we consider installing baseboard with a higher BTU output as well, per the comment "put in more heat emitters that will delivers the same btu with 120f water temperature"?
 
  #13  
Old 12-10-13, 06:57 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
Thanks Saves, that's what I wanted, I was actually playing Devil's Advocate... for you to cite your sources with some explanation. When a statement is made without any backup at all, it becomes difficult to sort the 'wheat from the chaff'. This is after all, the internet, where everyone is rich and famous, handsome or beautiful, and smarter than Einstein... right?

Old Guy, I'll stop by later and write more...
 
  #14  
Old 12-10-13, 10:37 AM
S
Member
Join Date: Oct 2011
Location: canada
Posts: 567
Upvotes: 0
Received 0 Upvotes on 0 Posts
Outdoor reset control

I agree we are all looking for our 15 minutes of fame. Oldguy a non condensing boiler must be protected from too low a return water temperature a four way motorized mixing valve is often used to protect the boiler while delivering the lowest possible water temperature to the heat emitters that will satisfy the thermostat. You are right the larger the heat emitters the lower the supply temperature can be and the 3 degree too 1% rule always applies .In my system I had a New Yorker oil boiler which was controlled by Tekmar and I sent the same water temperature as the gas condensing boiler does now only this low water temperature could not be sent to the bottom of the oil boiler.
 
  #15  
Old 12-10-13, 10:59 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
I'd expect Slant Fins to be warm to the touch but not convect or radiate any significant heat at that temperature
As long as they are warmer than the surroundings, they will still radiate heat... or course... but as you say, "...significant..." is the key word.

I would draw the 'significant' line with SF baseboard at about the 100F line.

With a conventional boiler, as below, you can't run water that cool anyway!

It's also posted we have a conventional cast iron boiler, not condensing
We know that one must be very careful running ODR with a conventional boiler that the BOIL MIN is not set so low that flue gas condensation becomes an issue. What good is saving a few bucks on fuel when the boiler/flue pipe/chimney is slowly being 'eaten' by acids and will fail prematurely? Read this as " BIG BUCKS TO REPLACE ".

should we consider installing baseboard with a higher BTU output as well, per the comment "put in more heat emitters that will delivers the same btu with 120f water temperature"?
This plays right into the "cost vs benefit" debate. Is it worth spending a ton of money on retrofitting the home with higher output baseboard to save a few bucks on fuel?

Let's get back to the unanswered questions from my first reply, as these have a strong bearing on the usefullness of ODR in your situation:

Do you have a savings expectation? How much? Have you weighed the possible savings against the cost of the ODR units to arrive at an expected payback period?

How good is your knowledge of the boiler water temperature now? i.e.

Does the water temperature consistently run above say 150F?

Has the boiler been installed long enough to have observed the behavior on the COLDEST days of winter and do you know what the water temperature was then?
You also said:

Each zone is about 75' (+/- 150' total)
This in all likeliehood means that your home is ALREADY "over-radiated" and there is little doubt that your boiler seldom fires to high limit in any case.

Being that you have about 75 feet in each zone means that your 'delta T' across the loop is probably greater than the 20F 'de facto standard' to which we usually design. There's about ten feet more than 'normal'.

So, if you've got a gas boiler, you want return temps to come up to 135F in a short time, and the boiler to run long enough to dry any condensation that has occured during the warm up period.

If you've got say 25F delta t across the loops, and you want the return to come to 135, then simple addition will tell you that you can't run the boiler less than 160F ... so your ODR is going to be limited to that 20F difference between 160 and the 180 high limit... which I'm willing to bet you never reach anyway.
 
  #16  
Old 12-10-13, 11:13 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
a four way motorized mixing valve is often used
Yes... along with constant circulation in the system...

Here's the thing though... mentioned in my previous post...

COST VS BENEFIT or ECONOMIC PRACTICALITY

To have the distribution system redesigned such that the system could be run with water from say 70 to 180 (or less if possible), the COST to have this work done would be quite a few thousand...

Where do we draw the line on what to spend versus what our savings expectations are?

How many years would it take to recoup the installation cost in fuel savings?

I say spend the money on insulation and air infiltration sealing. Keep the heat that you've paid for INSIDE. It's a MUCH bigger 'bang for the buck' IMHO.
 
  #17  
Old 12-10-13, 01:27 PM
T
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 65
Upvotes: 0
Received 0 Upvotes on 0 Posts
Interesting

It's a boiler that can accept a return temperature of 110F according to the promo literature and the manual states it has a high limit of 220F.

As stated earlier, the cost is offset by a $250 credit, use it or lose it soon. That's good incentive to try something that looks easy to install and might be a good thing to have.

I just don't know which to get; the one that plugs into the boiler, the one that plugs into the Taco box, or something else. The only difference I see between the two is warm weather shutdown. Others offer inside sensors and I don't know if that's good to have.

As far as insulating etc, we've had cellulose sprayed in the walls and insulated the basement rim. The old windows are reasonably tight, combined with the quality storms better than some new one's I've seen. It's a very big old house and without tearing it apart won't approach anything of modern day energy efficiency.

So which outdoor reset should we try?
 
  #18  
Old 12-10-13, 01:43 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
The only difference I see between the two is warm weather shutdown
Which to me is pretty much a 'non-issue'... really, how hard is it to turn the thermostat or the system OFF when the weather warms up? I just don't see the utility of that feature in a residential setting. Commercial, YES, I can understand it if tenants have control over t'stats...

I would probably base my choice on price, all other things being equal... so the PC 700 would win for me.

It's a boiler that can accept a return temperature of 110F according to the promo literature and the manual states it has a high limit of 220F.
I think if you were to carefully inspect the literature for the boiler, they still do not recommend continuous (or extended time) operation at that temperature. Some manufacturer information should be looked at with a jaundiced eye... and the 'fine print' carefully read.
 
  #19  
Old 12-10-13, 02:24 PM
T
Member
Thread Starter
Join Date: Dec 2012
Location: USA
Posts: 65
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thanks

Taco it is, thank you.

I pathetically stuck my head between the maze of pipes and read the return temp. Running supply is 170, return is 148 and the outdoor temp is 33. That sounds reasonable as a baseline and after installation will keep a watch on things.

While browsing the site, I came up with another question after looking into something. Clocking the gas meter I came up with 30.8 seconds for the 1/2 cf dial to spin twice with only the boiler on (no pilot lights elsewhere etc). According to a chart, that's about 116 cubic feet per hour and 116,000 BTU input. Is that what it should be for Burnham ESC4 boiler rated IBR 78,000, DOE 90,000 and BTU input of 105,000? Should those numbers be closer?
 
  #20  
Old 12-10-13, 03:33 PM
G
Member
Join Date: Oct 2008
Location: USA
Posts: 3,062
Received 24 Upvotes on 23 Posts
If the input rating of the boiler is 105,000 Btu/hr, the fuel you clock at the meter should be very close to that. But timing the 1/2 cf dial for two revolutions will not give a very precise number. You need to clock the meter for 10 minutes or so during a long heat call.

What are you using the gas heat content? - it varies a little, and should be shown as a correction factor on your bill.
 
  #21  
Old 12-10-13, 03:56 PM
T
Member
Join Date: Nov 2013
Location: USA
Posts: 35
Upvotes: 0
Received 0 Upvotes on 0 Posts
Pardon my ignorance but, why does the ESC4 need a Taco SR504EXP? Doesn't the Burnham IQ handle all the I/O needs for a 2 zone system?
 
  #22  
Old 12-10-13, 04:24 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Upvotes: 0
Received 8 Upvotes on 6 Posts
Doesn't the Burnham IQ handle all the I/O needs for a 2 zone system?
It can.

Depending on the configuration of the adjustable parameter of the controls, the DHW pump wiring and aquastat input can be configured to be used as a second zone. Of course this means that DHW can't be used, but if there are no plans to expand in that direction, yes... the second zone pump and thermostat could have been wired directly to the boiler.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: