AERCO Control System (ACS) - Manual (Page 105)

MC2: 04/23/13 Page 105 of 144
GF-131
AERCO Control System (ACS)
Installation, Operation, and Maintenance Manual
OMM-0081_0D
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, New York 10913 • Phone: 800-526-0288
APPENDIX C: RESET SCHEDULE AND
OUTDOOR RESET RATIO CHARTS
C.1 USING THE CHARTS TO DETERMINE RESET SCHEDULE
Each table in this appendix provides data for a specific building reference temperature. On the
vertical axis of each table are degree day temperatures. These are the average lowest
temperatures likely to be encountered. The engineer of your system should have this number
for your area. The reset ratio is shown across the top. The data in the tables is header
temperature. To determine the reset ratio for your installation, follow these steps:
• On the vertical axis, find the degree day for your area.
• Select the temperature that should be maintained in the header to maintain the building
at the desired temperature. The system engineer should have this information.
•
The proper reset ratio is the value found above the two selected points. For example, for
a degree day of 15°F and a header temperature of 125°F, the reset ratio is 1.4.
C.2 DETERMINING RESET SCHEDULE BY FORMULA
There are two steps required to determine reset schedule with this method. The first is to
determine the reset ratio by dividing the range of outside temperatures by the range of header
temperatures:
T
header
/T
outside
= Reset Ratio.
for example, If T
outside
varies from -10 to +95°F (105° range), and T
header
varies from 125
to 200°F (75° range), then the reset ratio equals
75°F/105°F = 0.714.
Once the reset ratio is determined, this number and the lowest or highest header temperature
and corresponding lowest or highest air temperature, are input to the following equation to yield
the building reference temperature:
T
heade r
- RR (TR-TO)+TR, where:
RR is the reset ratio
TR is the building reference temperature
TO is the minimum outside temperature, and
T
header
is the maximum heating system
Temperature desired at the minimum outside air temperature.
So in this example:
T
header
= 200°F
200°F = 0.714 [TR-(-10°F)] +TR
200°F = 1.714TR + 7.14°F
Solving for TR:
TR = (200°F-7.14°F)/1.714
TR = 192.86°F/1.714
TR = 112.5°F