HT# 059299-00 A
The starting reset ratio for most systems is the 100 (OD):100
(SYS) (Outdoor Temperature : Heating Water Temperature) ratio
This means that for every degree the outdoor temperature drops,
the temperature of the heating water will increase one degree
The starting point of the ratio is adjustable, but comes factory
set to 70°F Outdoor Temperature and 100°F Water Temperature
For example with a 100 (OD):100 (SYS) ratio, if the outdoor
temperature is 50°F, this means that the outdoor temperature has
fallen 20° from the starting point of 70°F Therefore, the heating
water temperature will increase 20° to 120°F (100°F + 20°F)
When controlling a none-condensing
boiler directly without the use of a
mixing valve, minimum boiler water
temperature must be set to boiler
manufacturer specifications In that
case, system temperature must not go
below such temperature
Each building has different heat loss characteristics A very well
insulated building will not lose much heat to the outside air, and
may need a Reset Ratio of 200 (OD):100 (SYS) (Outdoor :
Water) This means that the outdoor temperature would have
to drop 2° to increase the water temperature 1 degree On the
other hand, a poorly insulated building with insufcient radiation
may need a Reset Ratio of 100 (OD):200 (SYS) This means
that for each degree the outdoor temperature drops the water
temperature will increase 2° The Multi-MOD Platinum has
a full range of Reset Ratios to match any buildings heat loss
characteristics
A heating curve that relies not only on Outdoor temperature but
also on type of radiation will improve the comfort See the Building
Suggested Settings table for different types of radiation based on
an average building insulation and heat loss The contractor can
ne-tune these settings to the specic building need
Radiators (Steel & Cast
Iron)
100 : 100 0˚F
Baseboard (Finned copper
tube& Cast Iron)
100 : 100 0˚F
Radiant (High Mass/
Concrete)
400 : 100 -10˚F
Radiant (Low Mass/Joists) 200 : 100 -10˚F
Fan Coils & Air Handlers 100 : 100 20˚F
A Multi-MOD Platinum control that is equipped with Internet
communication is capable of using Heat-Timer space sensors to
ne-tune its outdoor reset operation while providing signicant
savings The Multi-MOD Platinum adjusts the target water
temperature based on the Space Feedback Gain and the
difference between the current Space Average and the Space
target Example: Using a Space Feedback Gain of 4, if the
Space Average is 70°F and the day target is set to 72°F, the
control will add 4° to the System Target temperature for every 1°
(ambient temperature) the Space Average is below the Space
Target In this example, it would add 8° to the target water
temperature to compensate for the 2° reduction in the Space
Average See "Space Feedback Gain" on page 47
If the Space temperature exceeded the Space Target by 2°
while the target water temperature is at the Minimum Target
temperature for an hour, the control will turn the boilers off until
the Space Average drops below the Space Target
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