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  1. #1
    hvtec is offline Regular Member - bad email address Contact Admin
    Join Date
    Jun 2001
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    Can someone explain to one who is ignorant what optimal start/stop is? I have a johnson Control Metasys system.
    Thanks

  2. #2
    Join Date
    Mar 2004
    Location
    Austin, Texas
    Posts
    1,959
    Optimal start will start the heating or cooling just the right amount of time before the schedule occupied time so the space will be at the setpoint at the scheduled time. In other words, on a very cold morning it starts earlier before occupied time than on warmer mornings.

    Optimal stop shut the system down BEFORE the scheduled unoccupied time and lets the building "coast" down. If the outdoor temperature is close to the set point it can shut it down much earlier than if the outside is very hot or very cold.

  3. #3
    Join Date
    Feb 2006
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    SouthEastern Virginia
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    Let me add that this algorythym looks at the day before and decides the aggressiveness of it's response. If the outside air temperature was 42 degrees yesterday morning then todays oss program will act according to that temperature.Because it was so cool it probably took a short time to cool the building so today the equipment will come on just before the occupied period.Well what if it were 70 degrees this morning and the building is going to take longer to cool down? The oss waited too long to start the occupied period because it used yesterdays numbers.See where you might get complaints in certain weather?It happens and by the time the tech gets to the jobsite the building has cooled down and you find the problem.It's the fine line between comfort and efficiency that we straddle to satisfy our customers.Hope this helps.
    By the way this is Trane's method of oss and other manufacturers may have a little different approach.Maybe some other reps will chime in if the have another explanation.

  4. #4
    Join Date
    Jan 2006
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    74

    Post

    If the system is an older Metasys system there is likely no Optimal Stop Start program. Within the older systems OSS was accomplished using the GPL tool or JC Basic. An OSS implemented in GPL is a tremendous amount of work (IMHO). The JC Basic route is much cleaner but if you live in the US, it's highly unlikely that any coding was done using the JC Basic tool. Most branches frowned on their engineers using the JC Basic tool because most of the technicians simply did not have the talent to understand it. If your in Canada - that's a different story.

    The DX9100 controller however has a very effective OSS algorithm built in. You can actually average all of your temperatures using the GPL tool and feed them into the DX9100 to process an OSS time. The only problem there is that the schedule would have to reside in the DX also. You could not access it from the Operator Workstation and make changes. You could however access the schedule from the very intuitive DX front panel display (LOL!). The DX is also handy for other things like adding 2 + 2 when you have an N30 for a front end - as the N30 is incapable of such higher math functions .

    Get yourself an NAE and you will have a pretty good Optimal Stop Start tool. It's easy to program and even works well! You'll have to get it from an authorized reseller or a Branch though as they don't sell them over the counter. Be sure to bring lots of money........

  5. #5
    Join Date
    Mar 2006
    Posts
    109
    You can access/modify the DX-9100 schedules from the OWS. Reference the OWS User's Manual, page 9-11.

  6. #6
    Join Date
    Jan 2006
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    74

    Smile

    I stand corrected 2^3. Thanks for the info.

  7. #7
    Join Date
    Dec 2007
    Posts
    23

    Continous Heating and Cooling

    The floor is designed in such a way that it would ask for heating and cooling at same time ( Solar heat on one side ). It is double ducted and VAV system. Could anyone please suggest me on this?

  8. #8
    Join Date
    Nov 2007
    Posts
    23
    Hope this will help From JCI

    The optimal Start/Stop object calculate the
    minimum time to bring a controlled zone
    temperature to a desired condition at occupancy
    with a heating or cooling plant; the module
    calculates also the optimal stop time to maintain
    the desired conditions up to the end of the
    occupancy time.

    The Optimal Start algorithm is adaptive as the
    heating and cooling thermal characteristics of the
    building are measured during the pre-heating or precooling
    cycles and used in the operations.

  9. #9
    Join Date
    Sep 2007
    Location
    Michigan
    Posts
    290
    Anyone else have to setup optimal START on a VAV system with say 30 zones, and have to look at all of them, not just pick one in the middle as some like to do. Engineer was being a stickler for his grand idea about not overheating or over cooling ANY space. If anyone is following me.
    "Yeah I can figure out whats wrong with it, but you were here first and there isn't room for two, plus it's cold up here, I'll be in the van"

  10. #10
    Quote Originally Posted by keepyoucool2003 View Post
    Anyone else have to setup optimal START on a VAV system with say 30 zones, and have to look at all of them, not just pick one in the middle as some like to do. Engineer was being a stickler for his grand idea about not overheating or over cooling ANY space. If anyone is following me.
    If they are fan powered with reheat, Heating is no problem individually using warmup without starting AHU since minimums are not in play. Cooling on the other hand would be damn near impossible or should I say take along time to balance/calculate and program out the cooldown cfm settings for all conditions in order to make it foolproof. It could be done. Anyway, He is the engineer. He is suppost to tell you.

  11. #11
    Join Date
    Sep 2007
    Location
    Michigan
    Posts
    290
    Quote Originally Posted by freddy-b View Post
    If they are fan powered with reheat, Heating is no problem individually using warmup without starting AHU since minimums are not in play. Cooling on the other hand would be damn near impossible or should I say take along time to balance/calculate and program out the cooldown cfm settings for all conditions in order to make it foolproof. It could be done. Anyway, He is the engineer. He is suppost to tell you.
    We know the engineer just knows what he wants, not what is pratical. AHU goes into warmup supplying all heat, lockout reheats. My idea was to use the warmup mode built into VMAs and they close down to warmup min CFM (I was thining 0) as the zone heats up, opposite of cooling. And as we approace the min AHU operating CFM, stop warmup. This would provide the fastest morning heat up. They didn't like that idea. I threw up my hands of trying to understand why they would rather take 3 hours to heat up all the spaces because warmup stops as soon as ONE zone meets setpoint.
    "Yeah I can figure out whats wrong with it, but you were here first and there isn't room for two, plus it's cold up here, I'll be in the van"

  12. #12
    Quote Originally Posted by keepyoucool2003 View Post
    We know the engineer just knows what he wants, not what is pratical. AHU goes into warmup supplying all heat, lockout reheats. My idea was to use the warmup mode built into VMAs and they close down to warmup min CFM (I was thining 0) as the zone heats up, opposite of cooling. And as we approace the min AHU operating CFM, stop warmup. This would provide the fastest morning heat up. They didn't like that idea. I threw up my hands of trying to understand why they would rather take 3 hours to heat up all the spaces because warmup stops as soon as ONE zone meets setpoint.
    So this guy would rather start a whole unit if only one zone needs warmup? and then shut it down if any one gets to setpoint? Doesnt sound very green to me. with a FPB, Heating max CFM should never be higher than min fresh air requirements for that particular space even when its occupied.You dont need any air from AHU in a warm-up situation at all. obviously a nonFPB needs a source of air for warmup but still overriding the reheats closed is crazy. Probably trying to disguise a underdesigned system or other issue that he screwed from the begining and doesnt want to admit it. This guy might as well not even bother with this. Hes wasting more than he thinks he is saving.
    unless he is trying to hide some other issue. Does this building recover quick and keep up good in really cold or hot weather?

    Freddy

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