Lochinvar MP2 - Manual (Page 8)

S TAGE D ELAY
The stage delay is the minimum time delay between the fir-
ing of stages. After this delay has expired the control can
fire the next stage if it is required. This setting can be adjust-
ed manually or set to an automatic setting. When the auto-
matic setting is used, the control determines the best stage
delay based on the operation of the system.
B OILER M ASS
The BOIL MASS setting allows the installer to adjust the
control to the thermal mass of the type of heat sources used
in the application. The BOIL MASS setting also adjusts the
minimum inter-stage delay time when operating with an
automatic differential.
Lo (1)
The Lo setting is selected if the boiler(s) that is used has a
low thermal mass. This means that the boiler(s) has a very
small water content and has very little metal in the heat
exchanger. A boiler that has a low thermal mass comes up
to temperature quite rapidly when fired. This is typical of
many copper fin-tube boilers. The Lo MASS setting pro-
vides the quickest staging on of boilers.
Med (2)
The Med setting is selected if the boiler(s) that is used has
a medium thermal mass. This means that the boiler(s) either
has a large water content and a low metal content or a low
water content and a high metal content. This is typical of
many modern residential cast iron boilers or steel tube boil-
ers. The Med MASS setting stages on additional boilers at
a slower rate than the Lo MASS setting.
Hi (3)
The Hi setting is selected if the boiler(s) that is used has a
high thermal mass. This means that the boiler(s) has both
a large water content and a large metal content. A boiler that
has a high thermal mass is relatively slow in coming up to
temperature. This is typical of many commercial cast iron
and steel tube boilers. The HI MASS setting stages on
additional boilers at the slowest rate.
D IFFERENTIAL
An on / off heat source must be operated with a differential
to prevent short cycling. With the control, either a fixed or
an auto differential may be selected. The boiler differential
is divided around the boiler target temperature. The first
stage contact closes when the supply water temperature is
½ of the differential setting below the boiler target tempera-
ture. Additional stages operate if the first stage is unable to
bring the supply water temperature up to the boiler target
temperature at a reasonable rate. As the supply tempera-
ture reaches ½ of the differential above the boiler target
temperature, stages are staged off.
Fixed Differential
If the user desires to have a fixed differential, this is set
using the BOIL DIFF setting in the ADJUST menu (FIG. 11).
Auto Differential
If the Auto Differential is selected, the control automatically
determines the best differential as the load changes. This
reduces potential short cycling during light load conditions
(FIG. 11).
SECTION C: PUMP OPERATION
S ECTION C1: P UMP O PERATION
P
RIMARY
P
UMP
O
PERATION
The primary pump operates under the following conditions:
• The control receives a boiler demand and is not in warm
weather shut down (WWSD).
• The control receives a DHW demand when DHW MODE
is set to 3 or 4.
• The control receives a set point demand and set point
MODE is set to 3.
Primary Pump Purge
After a demand is removed, the control continues to operate
the primary pump for a period of time. The maximum length
of time that the primary pump continues to run is adjustable
using the Purge setting. The primary pump continues to run
until either the purging time has elapsed or the boiler supply
temperature drops more than a differential below the boiler
minimum setting, see Figure 12.
8
FIG. 11