We've recently been running a lot of our sites using Siemens "start stop optimisation" which in residential terms is the same as adaptive recovery. SSTO is supposed to look at the paremeters you tell it to look at in order to start the units after night setback and bring the space temps to normal day mode settings by the time they are scheduled to be occupied. I have found that the system does not seem to be "learning" as it should and the units never seem to change their start times to compensate for weather changes. It currently takes an average time of 15 minutes to raise the space temp one degree. Anyone out there have any expierience with SSTO? Is 15 minutes per degree rise a resonable recovery rate? Night setback is about 5 degrees.
I use it all the time, just not on a Siemen system. How long has this been running like this? This 15 minutes per degree, is it trying to cool the space or warm it? Is their program set-up correctly and looking at the correct temperatures? Are the sensors reading accurately or influenced by anything affecting their readings?
You may need to trend the points you have entered into SSTO and make sure they are behaving as expected.
Are you using the Event Builder SSTO (GUI) or the PPCL SSTO (comand line)?
Siemens Apogee PPCL Start/Stop Optimization (SSTO) calculates to determine when a unit needs to be started. It looks at normal occupied start time, actual space temperature, outside air temperature and desired occupied heating & cooling setpoints.
It will calculate how long it will take to raise or lower the temperature. Each time the indoor or outdoor temperature changes the routine recalculates to determine start time. Those values then get applied to the calculation used for optimization and that is all based upon the season (heating / cooling)
You need to be careful when you are using SSTO, if there are points that are defined in SSTO that could be commanded by a different application, like Duty Cycling. They could interfere with each other.
There are multiple formulas used for SSTO, one for optimum start in the cooling season, one for optimum start in the heating season. If you are using optimal stop, there different formulas for that too.
Also do you know if you have adequate “look ahead time”. This is your EST (earliest start time) and LST (latest start time).
Do you have SSTOCO - which defines the thermal characteristics of your zone?
I have not worked on Siemens Apogee in about 6-7 years, so that’s the best I can do. If you need help with any statements or formulas let me know I might be able to help you.
Last edited by twisted pair; 02-23-2007 at 11:52 AM.
I'll look at the LST and EST values. I've been trending the points that I'm using for the set-up and that's where my concern started. Although the weather changes, the start time has stayed constant. I don't use the stop time function. That's some good info and I'll keep digging.
The 15 minutes per degree is warm up on an air handler w/ hot water coil. It's been running this way since installation, about 9 months. The points it's looking at are correct and so is the set-up. It's pretty basic in that respect.
Originally Posted by kwillmech
Originally Posted by dingman
Hi, Im interested in knowing the formulas and other relevant informations to implement ssto for ahu's and other equipment, would you be able to help me with these. Thanks in advance.
Hi twisted pair,
Originally Posted by twisted pair
I would really appreciate if you could help me with the formulas you mentioned, to implement ssto's. Once again, thanks.
The event builder version uses formulas built into the firmware. The Insight help menu has a good bit of information on SSTO. You can also look at the subpoints of the zone being used and it will show you the next calculated start time, etc. As far as I know theres not a set formula. I ask Siemens tech support and they refered me to the help menu also. The below program is what I use to show the calculated start times.
Lines 10 through 40 computes the number of days up to the beginning of the current month. Line 50 computes the number of minutes from the beginning of the year until midnight (the beginning) of the current day. Line 60 computes the possible start time in minutes after midnight. This value, however, could be 1440 minutes larger than it should if the year is a leap year. Line 70 tests for the 1440 excess and subtracts it if its there or uses the line 60 value as is. The result is divided by 60 to compute the time in a decimal value. Lines 80 and 90 compute the end time in a similar fashion to lines 60 and 70.
10 IF (MONTH .GE. 7) THEN GOTO 40
20 TABLE(MONTH,”YR_TO_FIRST”,1,0,2,31,3,59,4,90,5,120 ,6,151)
30 GOTO 50
40 TABLE(MONTH,”YR_TO_FIRST”,7,181,8,21,9,243,10,273, 11,304,12,334)
50 “YR_MIN” = 1440 * (“YR_TO_FIRST” + DAYOFM – 1)
60 STARTMQ = “ZONE_NAME:NX OCC TIME” – “YR_MIN”
70 IF (“STARTMQ”.GE.1440) THEN “STARTIME” = (“STARTMQ” – 1440)/60 ELSE “STARTIME” = “STARTMQ”/60
80 ENDTMQ = “ZONE_NAME:NX VAC TIME” – “YR_MIN”
90 IF (“ENDTMQ”.GE.1440) THEN “ENDTIME” = (ENDTMQ – 1440)/60 ELSE “ENDTIME” = ENDTMQ/60