Rheem Raypak MVB 1003A, Инструкция по установке и эксплуатации

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39
Outdoor Reset Concept
The Temperature controller can change the System Set
Point based on outdoor temperature (Outdoor Reset).
The temperature controller varies the temperature of the
circulating heating water in response to changes in the
outdoor temperature. The heating water temperature is
controlled through the modulation and/or sequencing of
the cascade. The Temperature controller can also control
the system circulating pump with an adjustable Outdoor
Cutoff.
When the outdoor temperature is above the Outdoor Cutoff,
the pump is turned off and no heating water is circulated
through the system. When the outdoor temperature
drops below the Outdoor Cutoff, the system pump relay
is activated and the heating water circulates through the
system. The temperature of the heating water is controlled
by the Reset Ratio, Water Offset, and changes with the
outdoor temperature.
Reset Ratio/Outdoor Reset
When a building is being heated, heat escapes through the
walls, doors, and windows to the colder outside air. The
colder the outside temperature, the more heat escapes. If
you can input heat into the building at the same rate that
it is lost out of the building, then the building temperatures
will remain constant. The Reset Ratio is an adjustment that
lets you achieve this equilibrium between heat input and
heat loss. The starting point for most systems is the 1.00
(OD):1.00 (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.
With the VERSA, both ends of the slope are adjustable. It is
factory set at 70°F (21ºC) water temperature (Boil START)
at 70°F (21ºC) outdoor air (OUT START), and 180°F (82ºC)
water temperature (Boil DESIGN) at 10°F (-12ºC) outdoor
air (OUT DESIGN).
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 2.00 (OD):1.00 (SYS)
(Outdoor: Water). This means the outdoor temperature
would have to drop 2 degrees to increase the water
temperature 1 degree. On the other hand, a poorly insulated
building may need a Reset Ratio of 1.00 (OD):2.00 (SYS).
This means that for each degree the outdoor temperature
dropped the water temperature will increase 2 degrees.
The VERSA Reset Ratio allows for full customization to
match any buildings heat loss characteristics. A heating
curve that relies not only on Outdoor temperature but also
on the type of radiation will improve heat comfort. The user
can fine tune these adjustments based on the specific
building need.
Reset Ratio Settings
The controller uses the four following settings to determine
the reset ratio:
1. Heater Start (Boil START). The Boil START temperature
is the theoretical heater supply water temperature
that the heating system requires when the outdoor
air temperature equals the OUT START temperature
setting. The Boil START is typically set to the desired
building temperature.
2. Outdoor Start (OUT START). The OUT START
temperature is the outdoor temperature at which the
control provides the Boil START water temperature
to the system. The OUT START is typically set to the
desired building temperature.
3. Outdoor Design (OUT DESIGN). The OUT START
is the outdoor temperature that is typical coldest
annual temperature where the building is located.
This temperature is used when completing heat loss
calculation for the building.
4. Heater Design (Boil DESIGN). The Boil DESIGN
temperature is the water temperature required to heat
the heater zones when the outdoor air is as cold as the
OUT DESIGN temperature.
Warm Weather Shut Down (WWSD)
When the outdoor air temperature rises above the WWSD
setting, the control turns on the WWSD segment in the
display. When the control is in the Warm Weather Shut
Down, the Dem 1 segment is displayed if there is a heat
demand. However, the control does not operate the heater
to satisfy this demand. The control continues to respond to
DHW demands.
Reset Ratio
The controller uses the following four settings to calculate
the Reset Ratio (RR). For example, when using the default
values, the RR is:
RESET RATIO =
(OUTDOOR START – OUTDOOR DESIGN)
(BOILER DESIGN – BOILER START)
RR = (70 - 10) / (180 - 70) = 0.55
Therefore, the RR is 0.55:1 (Outdoor : Water).
Decreasing Outdoor Temperature
Inc
reasing
W
at
er
Temperatu
re
Boil
START
OUT
DESIGN
Boil DESIGN
START
OUT
Figure 40. Reset Ratio
NOTE: The wiring diagrams in this manual show all
standard options. Refer to the large wiring diagram
provided with your heater for options installed on your
specific unit(s).