outdoor reset

Reply

  #1  
Old 05-08-14, 07:40 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
outdoor reset

I have noted there is a desire to use ODR on non condensing boilers . Don Pratt, formerly of Mestek Corporation ,an experienced hydronics trainer once told a group of heating contractors , Every boiler can be a condensing boiler. Pratt clarified his statement: Given the right operating conditions." During a cold start" condition, a small amount of intermittent flue gas condensation will form within the boiler. However , the operating conditions quickly increased the boiler to above the dew point and any initial condensate quickly evaporates. This situation occurs in every boiler during a cold start and is generally not a problem. If the heat dissipation exceeds heat production , thermodynamics demands that the fluid temperature in the system must drop until the rate of heat extraction by the distribution system equals the rate of heat production of the boiler.An ODR can be fully utilized by installing a system that unloads the boiler from the distribution system when ever the boiler temperature approaches a minimum operating temperature. A way to do this is to install a relay that keeps the boiler pump off when ever the burner is on but allows the pump with check valve to run when there is a call for heat and the burner is off. The wires from TT are moved to the ODR to create a heat demand and when the controller fires the burner through TT , the pump is shut off until the burner is off or the boiler water temperature reaches 140f and it is then safe to run burner and pump at the same time .I have done this on my steel boiler for five years with no sign of corrosion .There is a delay of water to heat emitters when the ODR is asking for water below 140f but does not impact comfort level. It is a very low cost solution to allow a noncondensing boiler to operate below 140f to maximize the ODR range .Note a check valve is a must to prevent water moving through boiler causing condensation when pump is off and burner is on .
 
Sponsored Links
  #2  
Old 05-08-14, 10:07 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Saves, please add a link to the page that you 'lifted' that information from.
 
  #3  
Old 05-08-14, 07:43 PM
G
Member
Join Date: Oct 2008
Location: USA
Posts: 2,995
Received 11 Votes on 11 Posts
l didn't follow the post, completely.
 
  #4  
Old 05-09-14, 08:38 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I don't really either Gil...

... I'm actually bordering on deleting the thread since it's obviously not a 'do-it-yourself' post, but rather a sort of 'news', or 'I just want to talk' posting... and that quote has come from another web page without credit to the author...
 
  #5  
Old 05-09-14, 08:41 AM
_
Member
Join Date: Dec 2010
Location: USA
Posts: 333
Received 0 Votes on 0 Posts
wouldn't it be a problem to operate in condensing mode for prolong period of time for a boiler that is designed to be a non-condensing boiler ?

regular boiler heat exchanger might be made out of the material that is not resistant to the acidity of the condensation (cast iron). exhaust piping might not be handling condensing flue gases well either. there is also no mechanism to evacuate the condensate from the boiler.

some regular boilers are designed to handle lower return temperature by injecting water in the exchanges in a specific way and using other tricks. but these very means are designed to avoid condensing, not to take advantage of it.
 
  #6  
Old 05-09-14, 09:14 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
The boiler is prevented from operating in the condensing range as the water flow through the boiler is prevented when burner is firing and boiler water temperature is below 140f. John Siegenthaler explains this as preventing the extraction of heat by the distribution system faster than the rate at which the boiler produces heat.
 
  #7  
Old 05-09-14, 09:38 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
You still haven't credited the web page that you've taken that information from. Would you do that please? If not, I'm going to delete the thread for sure...
 
  #8  
Old 05-09-14, 09:54 AM
G
Member
Join Date: Nov 2007
Location: MI
Posts: 2,634
Received 1 Vote on 1 Post
Why so quick on the Delete button? DIY can't exist in an information vacuum and this sounds like an interesting approach that could easily end up being a DIY project.
 
  #9  
Old 05-09-14, 10:16 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I agree... but the problem is that he 'lifted' copyrighted material from another website, posted as though it were his own, and gave no credit to the site or the author... that can't fly.

Am I 'quick' on the button? I don't think so... it's still here, isn't it?

Fair warning... going once......................
 
  #10  
Old 05-09-14, 10:41 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I have not taken this information from a web page and I gave Don Pratt credit for his observation that condensate is formed on a cold start , but soon is evaporated given the right operating conditions. The only reason I am sharing my use of a relay and ODR to create the right operating conditions for a standard boiler to delivery water to the heat emitters when the taraget temperature is below 140f is because of Global Warming. It has proved a simple and effective solution over using mixing valves and injection pumps and therefore more ODR should be installed as no pipe work is required.
 
  #11  
Old 05-09-14, 11:22 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
How come when I google parts of your original text I get hits in Google with the exact text?

Can you post a wiring diagram of how you connected the components.
 
  #12  
Old 05-09-14, 11:34 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
Do not know how to do that
 
  #13  
Old 05-09-14, 02:26 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
OK then, how about describing what equipment you used, and exactly how you wired it then?

If you can make me understand what you did, I'll do the drawing.
 

Last edited by NJT; 05-09-14 at 04:13 PM.
  #14  
Old 05-09-14, 04:12 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Here's what I think Saves is trying to describe...

Three running conditions:

1. HEAT DEMAND + BOILER UNDER 140 + BURNER ON = PUMP OFF

2. HEAT DEMAND + BOILER OVER 140 + BURNER ON = PUMP ON

3. HEAT DEMAND + BOILER UNDER 140 + BURNER OFF = PUMP ON

The first two conditions are that of a typical 'reverse' aquastat, a technique that has been used for like ever.

It's the third condition that is key to this technique of running a conventional boiler with a wider ODR range and not facing problems with condensation, but I believe there is a flaw in the logic... more on that later...

The thinking seems to be that the ODR can be allowed to target a temperature below the typical dew point (PLUS SYSTEM DELTA T) of the fuel being used because the pump won't be bringing cool water back from the system with the pump disabled during this condition.

Let's say ODR targets 130F --- Heat demand comes from ODR --- pump is disabled (boiler < 140) --- Burner fires and heats boiler to 130 but no flow in system --- boiler heats to 130 --- ODR kills burner --- heat demand continues because no water was flowing --- pump starts --- 130 water flows to system --- cool water back to boiler but no condensation because no combustion ---

Here's where the flaws start in my opinion:

Most boiler these days hold little water and will cool rather quickly once flow starts. This will cause the controls to kill the pump and start the burner again. How many 'extra' cycles will the burner have to burn? (read as extra wear/tear on system starting/stopping)

At best, this technique will gain you only the system delta T in extra ODR range because you STILL can't target a temperature lower than the actual dew point of the fuel being used. You'll STILL have continued condensation if you do. If you allow ODR to target a temp lower than the dew point, condensation will still occur inside boiler (and flue/chimney). In fact, flue/chimney condensation will still be occurring because the flue gases will be leaving the cooler boiler that much cooler. By the time they get to the top of chimney, they will already be well below dew point. Remember that flue gas temperature is directly proportional to the water temp in the boiler.

What sounds like a good idea at first sometimes fails after considering the big picture.

In other words, the down side to using this technique may end up costing more in the long run when you have to replace a chimney. I guess you could save the few dollars you don't spend on fuel in a piggy bank to use to repair the chimney... and then it's a wash, or a negative...
 
  #15  
Old 05-09-14, 04:14 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I used a Tekmar 256 and two 8 pin relays one with a 24 volt ac coil and the other a 120 volt coil.

The relay # 1 has a 24 volt ac coil operated by the end switches from zone valves.

The relay #2 is operated by power from b1 of aquastat .

Relay #1 pin 1 accepts power from c1 of aquastat.

pin# 8 accepts power from line.

pin # 3 is wired direct to pump.

Pin # 6 is wired to pin # 8 of 120v relay #2.

Pin # 5 is wired to pump.

Boiler was made cold start by removing blue wire from its terminal .

Operation of boiler is as follows .

Boiler water temperature above target temperature set by Tekmar.

A heat demand is created by an end switch closing and relay @ 1 is energized which closes N.O. contacts 8 and 6 pump is turned on.

Water in boiler cools to where Tekmar turns on boiler output and TT of aquastat is shorted,

B1 then sends power to burner and relay 2 pin 7 and N.C. switch pin 8 and 5 are opened and pump stops.

Tekmar sets a target above 140f burner is on pump is off until the boiler reaches temperature of aquastat low setting .

C1 is then powered and pump runs along with burner, until Tekmar opens boiler enable switch or high limit of aquastat is reached.
 

Last edited by NJT; 05-09-14 at 04:23 PM. Reason: added 'white space' for readability
  #16  
Old 05-09-14, 04:23 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
OK... to make my life easier, can you please identify either the exact model of relay that you used so that I can relate the pin numbers to the 'function'?

In other words, 'normally open', 'normally closed', 'common or arm' ..............
 
  #17  
Old 05-09-14, 04:30 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Also, please ID if the relays are SPST, SPDT, DPST, DPDT, etc... if you give the relay model, this will be clear.
 
  #18  
Old 05-09-14, 04:39 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
N.J. you of course are right modern boilers have less water and therefore promote burner cycling. They in my opinion need a buffer tank as pointed out by John Siegenthaler. My point is that there are a lot of older oversized boilers with lots of water in them that will benefit from ODR. If a mixing assembly that senses and reacts to boiler inlet temperatures can prevent condensation by slowing the water through the heat emitters until the boiler catches up so can shutting off the flow through the heat emitters and at less cost . I have an outside flue and after 5 year see no problems as my stack temperature is above 350f.
 
  #19  
Old 05-09-14, 04:44 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I have an outside flue and after 5 year see no problems as my stack temperature is above 350f.
You have a stack temp above 350 ? At what water temp are you seeing this ?
 
  #20  
Old 05-09-14, 04:46 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I don't have a relay here but pin 1&3 N .O. ,pin 1&4 N.C. pin 8 & 5 N.C. pin 8 & 6 N.O. pin 2 and 7 are the coil .
 
  #21  
Old 05-09-14, 04:50 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I will have to hook up the flue and fire the oil boiler to tell you this as I converted to gas last year , a condensing boiler.
 
  #22  
Old 05-09-14, 05:28 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I don't have a relay here but pin 1&3 N .O. ,pin 1&4 N.C. pin 8 & 5 N.C. pin 8 & 6 N.O. pin 2 and 7 are the coil .
So in other words;

they are all DPDT relays.

pole 1: 1 is common, 3 is NO, 4 is NC

pole 2: 8 is common, 6 is NO, 5 is NC

Is that correct?
 
  #23  
Old 05-09-14, 05:39 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
OK, I think I've got it... two more questions though...

You are only using ONE pole of relay 2 ? second pole (1,3,4) has no connections?

I presume that the 260 is getting it's heat demand from the endswitches as well? In other words, the 24VAC that powers relay 1 is also going to the 260 ?
 
  #24  
Old 05-09-14, 08:42 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,481
Received 5 Votes on 4 Posts
I don't like the idea at all. It was fine a decade or so ago when boilers had more water volume. Cast iron boilers stress due to quick temperature changes. Years ago they also used system bypasses and still do commercially. Today the use of a boiler bypass is more popular.
I don't lime heating the boiler up, turning on a pump and slamming cold or cool water into the low water volume water boiler. Shut down the pump re-heat the boiler turn on the pump and cool the boiler quickly over and over again. Again larger water volume boilers it was not as much issue due to the amount of water volume, now the volume is much less.
What was OK years ago may not be good today due to changes in the products.
 
  #25  
Old 05-10-14, 07:22 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
You make a good point using my method of control on newer boilers and cast iron boilers ,never could see the advantage of cast iron over steel .In my opinion these low water content boilers need a buffer tank to add some place to store btu and limit burner short cycling .Hopefully when a new noncondensing boiler is installed today it is equipped with a mixing valve that adjust the flow through the heat emitters so boiler can keep up with heat flow and prevent condensation in heat exchanger. My control is not the best only cheapest , I have them on three boilers all steel older oil boilers .
 
  #26  
Old 05-10-14, 02:16 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
How about answering the questions in post #23 ?
 
  #27  
Old 05-10-14, 05:39 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I found my wire schematics and I made a few mistakes .I will try again. Both relays are 24 volts, 1 End switches connected to Tekmar at terminal 9 & 7 . 2. transformer connected to Tekmar terminal 9 & Relay 1 terminal 2 . 3 Tekmar terminal 8 connected to other side of transformer powers up Tekmar. 4 When end switch closes circuit is made through switch to tekmar terminal 7 and to relay 1 terminal 7. Terminal 2 connects to other side of transformer . Heat demand is generated at Tekmar and target temperature is set. 5 Relay 1 terminal 1 accept wire from TT of aquastat . terminal 3 accepts other wire from TT 6 Relay 1 terminal 8 accepts line voltage terminal 6 connected to relay 2 terminal 8 . Relay 2 terminal 5 connects to pump. 7 Relay 2 terminal 1 accepts power from B1 of aqua stat . Relay 2 terminal 3 connects to burner . 8 C1 of aqua stat wires directly to pump.
 
  #28  
Old 05-10-14, 09:01 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I give up.

I don't like the idea anyway.
 
  #29  
Old 05-10-14, 09:38 PM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
I tried , may be some one else would like to try it .
 
  #30  
Old 05-11-14, 06:02 AM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,481
Received 5 Votes on 4 Posts
The need for a buffer tank on a cast iron or steel boiler is normally used for an oversized boiler not a properly sized boiler. A correctly sized cast iron or steel boiler will give you longer run times. Either boiler may require boiler protection against flue gas condensation when properly sized and less chance if oversized as most boilers are.
 
  #31  
Old 05-11-14, 08:42 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
John Siegenthaler, P.E. has an article in the HPAC March issue in titled Do Not Go Unprotected , page 32 . The main point I get from his article is that to control condensation from forming the mixing valve must measure the water temperature entering the boiler and be able to react to maintain inlet temperature above a pre selected minimum value. He also states ", Just stick with the same principle of measuring boiler inlet temperature and reacting to it by not allowing the distribution system to extract heat from the water flowing through it faster than the rate at which the boiler produces heat". In my opinion that is what my control system does .
 
  #32  
Old 05-11-14, 09:29 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Saves, why not provide links to the articles that you are reading, and let others decide for themselves based on reading the entire article rather and 'cherry picked' statements?

Here is the original article, courtesy of HPAC magazine:

http://www.hpacmag.com/digital-editi...E-03012014.pdf

Thank you for finally providing your source, as I asked much earlier.

I tried , may be some one else would like to try it .
I guess you did... but if you want your ideas to be understood, you need to explain it so that even an id10t like me can understand it. Your descriptions of the wiring are obtuse and unclear, IMHO.

Try using 'white space'... adding paragraphs and such... it might help.
 
  #33  
Old 05-11-14, 09:33 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
In my opinion that is what my control system does .
I don't really agree with that.

What 'your' control system does is start and stop the burner, adding wear and tear to burner components, and thermally stressing the boiler... endlessly... in an attempt to squeeze a few degrees of the outdoor reset temperature range.

My opinion is that the net result is going to cost more in the long run on repairs than the fuel you are saving... but it's just an opinion, like yours, and we're entitled to our opinions.

Your mileage may differ, or you may convince yourself that it does.
 
  #34  
Old 05-12-14, 01:42 AM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
The following is from a residential system I installed in 1973 as an oil burner. It had a physically huge steel firebox-fire tube boiler. Some years later the boiler was replaced with a much smaller vertical fire tube model and run for a season burning oil and then converted to gas.

I had two thermal switches on the boiler, a cut-in temperature and a cut-out temperature. There was a third, manually reset high temperature safety shutdown but that is not pertinent to the story. Obviously the large firebox-fire tube boiler held a lot of water and while the vertical fire tube boiler held considerably less it was sill a significant amount of water compared to the residential boilers of today.

I had the cut-in temperature set at about 140 degrees (all temperatures in Fahrenheit) and the cut-out temperature set at about 170-180. The burner would only fire IF the circulator relay was closed and the temperature was below the cut out setting. The burner would only initiate if the temperature dropped to the cut-in temperature with the circulator running. To explain in more detail, if there was a "call for heat" when the boiler temperature was, say, 150 degrees the burner would NOT initiate until the temperature dropped to cut-in, 140 degrees. The burner would then continue to run until lit reached the cut-out temperature (which was extremely rare) or until the circulator relay opened (room thermostat satisfied, ending the call for heat) stopping the circulator. The result was that often times the room thermostat would close, starting the circulator but with the boiler temperature above cut-in the burner would not ignite and a few minutes later the room thermostat was satisfied, the circulator stopped and the boiler never fired at all.

Now when the stored heat in the boiler water was not sufficient to satisfy the room thermostat the boiler temperature would drop below cut-in (140 degrees), the burner would fire as long as the room thermostat was calling for heat (circulator running) and there would be a gradual rise in water temperature. As I recall all these years later the normal temperature range in the boiler was between 140 and 160 degrees, higher in colder weather and lower in warmer weather so in effect the water temperature WAS "modulating" in accordance with the outside temperature. It could also be stated that the system water temperature was modulating, albeit to a lesser degree, based upon the heat loss of the house. It was a very simple system and it worked very well. I also had a selector that would allow the burner to continue operation after the circulator was stopped for use in very cold weather. Under this control scheme the burner would initiate as always but then continue to the upper operating limit (170 degrees or so) in order to have a bit quicker response during extremely cold (for the Seattle area) weather. That scheme was never used, even with outside temperatures in single digits.

Again I stress, this was a system that had a large amount of water compared to today's residential boilers. It was also a system that had been designed and installed in accordance with the ASHRAE manual J heat loss calculations. The input from the gas burner was about 40,000 BTU/hr. Nonetheless, I see no reason why some adaptation of this system could not be used on a low-mass system provided the system was properly designed for the heat loss.
 
  #35  
Old 05-12-14, 05:42 AM
S
Member
Thread Starter
Join Date: Oct 2011
Location: canada
Posts: 567
Received 0 Votes on 0 Posts
Furd I see you were thinking out side the box and the result was burner off as long as possible and burner on as long as possible. Result of this control less burner short cycling .
 
  #36  
Old 05-12-14, 05:03 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
No, the burner on time is not necessarily longer unless the extreme cold option was allowed by changing the selector switch. Normally the burner would go off when the room thermostat was satisfied BUT the burner was always inhibited from starting unless the boiler temperature fell to the cut-in setting. Because of the relatively large mass of water in the boiler it was often possible to have two or three heat calls satisfied with just the stored heat in the boiler. What truly made the system economical to run was the fact that it was right-sized to the house.

When the gas company had contractors replacing the roughly 100 year old buried gas distribution piping (late October as I recall) the heat was off for most of the day. My mother called me because she was cold and I caught one of the contractors just as they were finishing up for the day. I told him to turn the gas back on and he refused, stating that I had to call the gas company and THEY would send someone. When I called, the gas company told me the contractor would turn it on. I turned it on myself, bled the air from the line and let 'er rip. Since the burner had a spark ignition I wasn't worried about about a pilot failure. It took several hours to bring the house back up to normal temperature but it would also keep the house comfortable during the coldest temperatures experienced in Seattle.

This is why I always advocate for the largest differential setting possible while still keeping a boiler hot enough to preclude fire-side condensation. Also, there are seldom any good reasons to fire the burner when the circulator is not running. Just add the feature that the burner cannot initiate until the boiler temperature drops to cut-in would save a bundle.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


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