[TRNSYS-users] How to use Type 84 properly

[Jeff Thornton]

<Hi everyone,I am trying to connect a chilled ceiling to a moving average
from the last 3 days.If the average ambient temperature is lower than 16
degrees for 3 days in a row, the input temperature for the chilled ceiling
should go up to 24 degrees.  I am using Type 84 for that, but I am not
sure about my input value(how to connect my moving average to my ambient
temp) and how my equation for this should look like.I had the idea of a
'greater than/lower than' equation but I can only turn it on and off with
this one.  Can anybody help??>

Leo,

I'm not sure a moving average is going to help you in this case as the
average doesn't capture the effect you're looking for.  For example,
imagine you has two really cold days followed by a warm day.  In the logic
you described above, the chilled ceiling would go up to 24 degrees when it
shouldn't (as the third day is warm).  What you need to do is use a
run-time calculator in conjunction with a daily integrator or run-time
average to better implement your control.  Use the moving average to
calculate the average over the last 24 hours, feed that to an equation of
the form:

Variable=LT(T_Moving_Average,16)

Then feed the result of the Variable equation (a one or a zero) to a
run-time calculator and the output from the run-time calculator to another
equation:

OK_24=GT(Runtime,72)

Then use this equation as the control for your chilled ceiling.

Jeff


Jeff Thornton
President - TESS, LLC

22 North Carroll Street - Suite 370
Madison WI 53703 USA

Phone: 608-274-2577
Fax: 608-278-1475
E-mail: thornton at tess-inc.com
Web: www.tess-inc.com