Hello eQuesters,
I am trying to model a two pipe system with a demand operation loop for a
residential building in Maryland. Currently, my two pipe system turns on
cooling when the zones are calling for cooling as expected, however it
never changes over to heating during the winter. It is always either off,
or on very rare occasions cooling, resulting in high unmet heating hours.
Can some one explain how the two pipe system determines when to change
from heating to cooling mode?
I've looked at the zones they are definitely below the heating throttling
range. Does eQuest take a sum of the room loads on the loop to determine
to heat or to cool?
Your help is greatly appreciated.
Thanks!
Justin
I usually use a snap function to specify when the loop is in heating /
cooling:
By the way, I've modeled a few 2-pipe systems (in the DC area) before,
and it is nearly impossible to get the unmet load hours below 300 for
the average building (without significantly relaxing the thermostat
setpoints, or having supplemental heating/cooling systems). Hopefully
you are not modeling this for LEED purposes!
James Hansen, P.E., LEED AP
I could model it as snap, but I would still get some unmet hours for
certain days. So far modeling as demand operation seems to be satisfying
the thermostat settings in the summer, but I just can't figure out why
heating isn't turned on. And the model does have to meet LEED
requirements.
Justin,
"Demand" is not adapted to 2-pipe loops. You should use either "Snap" or "Scheduled".
Note that as James pointed out, it is very difficult to figure out the correct changeover period (if it exists!) when using a schedule.
Regards,
[cid:image005.jpg at 01CE2407.2CA11BD0]Demba Ndiaye, Ph.D., P.E., LEED AP BD+C, BEMP
It has been a few years since I have used DOE-2.2 day to day.
I recall that the hours where loads (temperatures) not met are reported include any optimum start / night purge hours. So if you have optimum start in your schedules you would typically get a few hundred hours reported even though conditions are being met during what we would call established building hours (i.e. hours when comfort conditions are expected). As long as night purge / optimum start existed you would never be able to zero these hours.
I am unsure whether this has been tidied up in the most recent versions and I am also unsure whether it is across all SS reports. If I recall correctly SS-R, SS-F and others were affected in this way.
Regards,
Graham
It’s just great to see people caring for this topic. I found it insightful in so many ways. This information should be educative for more categories of people.