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  1. #14
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    Quote Originally Posted by Juan Madera View Post
    Are you making hot water with this boiler as well?
    No. Just heating water for the building heating system.

  2. #15
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    Quote Originally Posted by comfortdoc View Post
    It's time to hire a professional to assess the entire system and explain how it operates. The best anyone on this forum can do is offer educated guesses based n your descriptions. The downfall is that we have no idea exactly how each component the system was designed to interact with the others. There are several ways hat system could have been designed and each will operate differently. Incorrect setup could lead to increased energy usage and decreased comfort.
    Yes, I might need to get a professional HVAC engineer in to look at the system.

    Right now I'm only trying to get some ideas about how to set up the Tekmar controller to run the boiler as efficiently as possible. Then I will discuss my ideas with the technicians that maintain the system.

    If the technicians explain to me why it's not possible to run the system closer to the minimum inlet temperature of 105F, I will then consider bringing in an HVAC engineer and/or modifications (bypass valve).

    By the way, I am a mechanical engineer myself. I don't have much experience with HVAC, so I'm not qualified to work in this field. But I have a better understanding of how heating systems work than the average person.

  3. #16
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    Quote Originally Posted by beenthere View Post
    They would use -36 or -40 if the published temp was -36.3°F

    Has the HOA or condo association put you in charge o reducing cost? Remember, one slip up and you could cost them a lot more money replacing a broken/rotted out boiler, and no heat for a week or so.
    We have a small building, only 12 owners. I've lived in the building for 20 years. I've decided myself to look into trying to make the heating system operate more efficiently. Right now the Tekmar is set for 155 F minimum supply water temperature, but the boiler can operate down to 105 F return water temperature. So it seems like there is room for improved efficiency by dropping that minimum temperature setpoint lower, which would allow the system to run at lower temperatures during higher outdoor temperatures.

    I'm actually a mechanical engineer, but not much HVAC experience. I'm aware that mechanical systems are always far more complicated than they appear to the untrained eye. So I plan to discuss any ideas I have with the technicians who operate the system before making any changes.

    The boiler may have been set to 150 min to allow for heat loss in the piping, and or the GPM through the furtherest fan coil/heat emitter.
    OK, noted. I am considering monitoring the system over several months, recording the supply, return and outdoor temperatures to get some data on how the system performs.

    I figure the worst case is probably first thing in the morning when everybody gets up and starts turning their thermostats on. That's probably when the lowest return temperatures occur.

    Copper tube aluminum finned baseboard heat out put drops a lot if the average water temp drops below 140 in them. So lowering the water temp below 150 could cause some of the other units to not heat up as well or as warm as they should.
    OK, noted.

    I believe the Tekmar controller adjusts the supply temperature along a curve, not a straight line. So the reduction in supply water temperature is more towards the higher outdoor temperatures. Perhaps Tekmar did this for the reason you mentioned.

    Plus, when the boiler water temp is lowered, you lower the temp that they are allowed/able to keep their condo. So you would need to find out how warm all of the other condos keep their condo, before lowering the water temp.
    Ya, I've thought about this. We had extra insulation added to the exterior walls of the building 13 years ago, so I'm thinking we might be able to lower the design point water temperature to 170 F, from the current set point of 180 F (which is also likely the original design temp when the build was built). If some owners complained about not getting enough heat on cold days, we could always just put it back up to 180 F.

    At what outdoor temp does the reset start increasing water temp?
    It depends on what the minimum supply temp is. Right now, with the minimum supply temp set at 155 F, and estimating using the curve in the Tekmar manual, it looks like it doesn't start increasing the water temp until about 4 F.

  4. #17
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    Why would the system delta-T change as a consequence of the outdoor ambient? The system would have no awareness of the outdoor ambient. The system delta is the result of system heat loss to the conditioned space - where the temperatures would be fairly constant, no? So why would the delta ever vary?

    You don't seem to have a grasp of how the boiler reset operates. The reset control varies the boiler temperature inversely to the outdoor ambient in accordance with the reset ratio. The system delta would only be slightly indirectly altered.

    Or am I missing something important? <g>

    PHM
    -------




    Quote Originally Posted by nielkfj View Post
    I was thinking about doing that. But the ∆T changes with the outdoor air temperature, doesn't it?
    This is how I understand it:
    At "Coldest Outdoor Temperature" (design point), ∆T is at a maximum.
    At an outdoor temperature equal to the design room temp ∆T=0.

    So the ∆T should change along a straight line as the outdoor temperature changes. Correct?

    The critical point seems to be at the lowest outdoor temperature that the Tekmar calculates the target supply water temperature to be "BOIL MIN", the minimum allowable supply water temperature. So I would need to measure the ∆T when the outdoor temperature is at this point.

    At higher outdoor temperatures the Tekmar will calculate a higher target supply water temperature along the ODR curve. The ∆T will increase, but the supply water temperature should increase more, so there is less risk of going below the minimum return water temperature.



    Yes, I should be able to find that.
    So when these heating systems are designed do HVAC engineers use the actual published data for the coldest outdoor temperature, for example -36.3 F? Or do they use an assumed value at a convenient number, like say -20 F, -30 F or -40 F?



    OK, noted.

    I've also seen 180 F mentioned in other things I've read. It's the default value used for "Fin-tube convectors" in the Tekmar manual. So, it would probably be a pretty good assumption that this is what the original designers used.

    An indoor temperature of 70 F also seems to be pretty common from what I've read. So I guess it would also be a pretty good assumption that this is the value used in the original design.

    One thing I forgot to ask in my first post is what differential temperature (∆T) is typically assumed at the design point (coldest outdoor temperature) when these systems are designed?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #18
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    Quote Originally Posted by bobboan View Post
    As I mentioned, the boiler water temp must be kept at 140* or higher to prevent flue gas condensation which would rot the boiler and flue. The manufacturer's number of 105* has nothing to do with that; it's simply the lowest RWT that the boiler can withstand to prevent thermal shock. The 140* number would apply to any atmosepheric gas boiler.
    Actually the boiler I&O manual states that the minimum of 105 F is to prevent condensation. Here is a screen capture of the caution from the Raytherm Models 0181-4001 Type H boiler I&O manual:

    Name:  Raytherm Caution_sm.png
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    I have also confirmed with Raypak that the 105 F minimum is applicable to the 12-year-old version of the boiler model that we have. Apparently there is something about the design of this boiler that allows it to operate at a lower inlet water temperatures.

    Regardless, your point is noted. So, is 140 F the typical minimum inlet water temperature for older or most other non-condensing boiler designs?

    I suspect the technicians maintaining the boiler are unaware of this lower operating temperature capability and have assumed a higher minimum temperature such as 140 F.

    Apparently the flue is a 14"∅ "class B" flue, which I think means it has a double wall. It goes right through the center of the building - it isn't exposed to outdoor temperatures until the last ~3 feet above the roof. So I figure it should be kept pretty warm, although the gap between the double walls might be ventilated which could cool down the center tube. Do you think condensation could be an issue inside this flue?

    Also, how does lowering the inlet water temperature to the boiler cause condensation inside the flue? I figured the combustion gasses would be so hot that they would still be well above their dew point coming out of the boiler even if the inlet water temperature to the boiler was say 30 F lower.

  6. #19
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    The cooler/colder the water is, the more heat it removes from the combusted gas. So the combusted vapors going into the chimney are much cooler. A chimney with 275°F vapors entering it, may work okay for a 10' chimney, but cause condensation in a 30' chimney.

    A boiler efficiency test is best done when the water is nearing the boilers set water temp, which is when the return water is also near its max return temp.

    Check the delta between the boilers return and supply water temp. Also see if you can find the GPM going through it. Are the heating water valves 2 or 3 port valves?
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  7. #20
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    Rather then concentrating on the boiler and make up air units in this building concentrate on the "Building" itself. Tightening the envelope has a much higher return on investment.

  8. #21
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    Quote Originally Posted by Poodle Head Mikey View Post
    Why would the system delta-T change as a consequence of the outdoor ambient? The system would have no awareness of the outdoor ambient. The system delta is the result of system heat loss to the conditioned space - where the temperatures would be fairly constant, no? So why would the delta ever vary?
    This is how I see it:

    As the outdoor temperature increases, there is less heat loss from the "conditioned space" (or building) to the outdoors. So as a consequence the conditioned space draws less heat from the heating system in order to maintain the desired temperature. Hence the water returning to the boiler is at a higher temperature - in other words a smaller ∆T.

    At the extreme, when the outdoor temperature is the same as the desired temperature of the conditioned space, there is no heat loss from the space, the conditioned space draws no heat from the heating system, and the water returning to the boiler is at the same temperature as the supply water - ∆T = 0.

    You don't seem to have a grasp of how the boiler reset operates. The reset control varies the boiler temperature inversely to the outdoor ambient in accordance with the reset ratio. The system delta would only be slightly indirectly altered.

    Or am I missing something important? <g>

    PHM
    -------
    The only education I have about outdoor reset is from reading the Tekmar 261 operating manual last week, so likely there are a great number of things that I don't understand. I don't know much about reset ratios, just a bit I read on the internet.

    I do understand that the ODR controller decreases the boiler supply water temperature as the outdoor temperature increases, and vice versa. The method used to calculate the supply water temperature based on the outdoor temperature could be reset ratios which I understand is a straight line change in temperature inversely proportional to the outdoor temperature, as you said. Or it could be calculated according to a formula - a curve instead of a straight line - which is apparently what the Tekmar controller does.

  9. #22
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    Quote Originally Posted by beenthere View Post
    The cooler/colder the water is, the more heat it removes from the combusted gas. So the combusted vapors going into the chimney are much cooler. A chimney with 275°F vapors entering it, may work okay for a 10' chimney, but cause condensation in a 30' chimney.
    OK, noted. This could be the reason why the technicians have set the minimum supply temperature to 155 - to prevent condensation in the flue.

    I think I understand what you mean about the 30' flue. The flue gasses will lose heat as they travel up the flue. The longer the flue, the more heat will be lost. So heavier vapours could start to drop out if the flue gas temperature gets too low.

    A boiler efficiency test is best done when the water is nearing the boilers set water temp, which is when the return water is also near its max return temp.
    But the efficiency should be higher when the return water temperature is at a lower temperature, no? This is part of what makes outdoor reset more energy efficient, isn't it?

    Check the delta between the boilers return and supply water temp. Also see if you can find the GPM going through it.
    Ya, if I do start to record the performance of the system, I'll note the supply, return and outdoor temperatures.

    I don't think I can get the GPM. The system has a single centrifugal pump, so I would need the curve and ∆P across the pump. There are only pressure gauges on the inlet line to the boiler and the boiler itself.

    Are the heating water valves 2 or 3 port valves?
    Not exactly sure what a "heating water valve" is. If you mean the zone valves in each apartment, these are all 2 port throughout the building.

  10. #23
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    Quote Originally Posted by pecmsg View Post
    Rather then concentrating on the boiler and make up air units in this building concentrate on the "Building" itself. Tightening the envelope has a much higher return on investment.
    OK, noted.

    However, I think the envelope is already pretty tight. The siding was replaced in 2006, and extra insulation was installed at that time. Also new windows were installed at the same time.

    One area that we could make more efficient is two "cabinet unit heaters" that sit inside of the two main entrances. These heaters have no thermostat connected to them, they just have a manual rheostat that controls the fan speed, hot water runs through them continuously whether the fan is on or not. People just turn them on and off and adjust the fan speed to whatever they think is appropriate and leave it.

  11. #24
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    Quote Originally Posted by nielkfj View Post
    OK, noted. This could be the reason why the technicians have set the minimum supply temperature to 155 - to prevent condensation in the flue.

    I think I understand what you mean about the 30' flue. The flue gasses will lose heat as they travel up the flue. The longer the flue, the more heat will be lost. So heavier vapours could start to drop out if the flue gas temperature gets too low.



    But the efficiency should be higher when the return water temperature is at a lower temperature, no? This is part of what makes outdoor reset more energy efficient, isn't it?

    It is higher. But when the burner has only been on for 5 minutes, the flame and flue draft still aren't always completely stabilized, and the test result is false.


    Ya, if I do start to record the performance of the system, I'll note the supply, return and outdoor temperatures.

    I don't think I can get the GPM. The system has a single centrifugal pump, so I would need the curve and ∆P across the pump. There are only pressure gauges on the inlet line to the boiler and the boiler itself.



    Not exactly sure what a "heating water valve" is. If you mean the zone valves in each apartment, these are all 2 port throughout the building.
    The pump should have a tag on it somewhere listing its rated GPM at X feet of head. Most likely the system was engineered, and the circ was selected to meet the specs of the engineered system. So you can probably just used the pumps listed GPM.
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  12. #25
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    Quote Originally Posted by beenthere View Post
    It is higher. But when the burner has only been on for 5 minutes, the flame and flue draft still aren't always completely stabilized, and the test result is false.
    I think I see what you are saying now. You were explaining that when the return water temp reaches a maximum when the system has stabilized.

    I was explaining something different, that if the set water temp is lower, the boiler efficiency will be higher.

    The pump should have a tag on it somewhere listing its rated GPM at X feet of head. Most likely the system was engineered, and the circ was selected to meet the specs of the engineered system. So you can probably just used the pumps listed GPM.
    OK, noted - will check the pump tag (nameplate).

    Actually, I have the original design drawings for the mechanical systems in the building. However, I am a bit sceptical that the information is accurate because they are an "Issued for Building Permit and Tender" revision, not "As-Built". There are also some differences between the drawings and what actually exists in the building now.

    In any case the information stated on the drawings for the "Radiation Water Pump" is:
    Flow: 50 gpm
    Head: 18 ft
    Power: 1/8 hp

    The existing pump is not original, and I believe has been changed several times over the years. So who knows what specs were used in selecting the existing pump. But if the tag indicates is the close to the same flow rate and head as stated on the drawings, I guess I could assume that the figures are reasonably accurate, or at least in the ball park.

  13. #26
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    That boiler is allowed a max GPM of 90 GPM, and a min of 40 GPM.

    Its a low temp rise boiler.
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