LG Multi V mini Engineering Manual page 51

unit or consider a Multi V water-cooled alternative. These strategies
are common on air-cooled projects in northern climates to eliminate
"extreme" over-sizing of the outdoor unit(s).
Limit the surrounding outdoor unit air temperature by providing a
ventilated equipment enclosure equipped with an auxiliary heat
source. On heating days, the auxiliary heat source will provide the
building engineer the ability to temper and control the minimum air
temperature surrounding the outdoor unit(s). On extremely cold
days, it may be more advantageous to operate the auxiliary heat-
ing equipment and limit the minimum ambient temperature in the
enclosure in lieu of investing additional capital to install an extremely
over-sized and de-rated Multi V outdoor unit. The enclosure also
eliminates the potential operational problems caused by snow and
ice. During the cooling season, the outdoor unit(s) will be protected
from the adverse effects of direct sunlight.
After selecting an outdoor unit model and the outdoor unit's cor-
rected cooling and heating capacity has been determined, there may
be additional capacity correction factors to consider.
In Cooling mode, two correction factors may apply—one for the ele-
vation difference between the outdoor unit and the indoor unit(s) and
a second for the altitude above sea level. If the corrected cooling
capacity was manually calculated, apply the appropriate elevation
difference factor found in either Table 15 or Table 16 on page 56
(choice of table depends on the architecture of the system design).
Multiply the manually calculated outdoor unit corrected cooling ca-
pacity by the elevation difference correction factor. If the corrected
cooling capacity was derived from the LATS report, this elevation
difference correction factor was already applied to the system design
by LATS and no action will need to be taken.
If the system is installed at a significant elevation above sea level,
the outdoor unit capacity will be affected by air density. Apply the
appropriate altitude correction factor for the building's location to
the outdoor unit capacity. The result is the actual corrected cooling
capacity of the outdoor unit after all potential correction factors are
considered.
After applying the appropriate cooling correction factors to the
outdoor unit, verify the actual cooling capacity is at least equal to the
total building load (considering building diversity, if applicable).
Next, determine the outdoor unit's actual corrected heating capacity.
Two correction factors may apply—one for operating the outdoor unit
with frost on the coil, and one for altitude above sea level. The im-
pact of frost accumulation on the outdoor unit coil can be calculated
by LATS or manually by the system designer. In certain weather
conditions, frost may form and accumulate on the air-cooled outdoor
unit coil at design day conditions. If design day conditions are below
the dew-point of the surrounding air, frost is less likely to form on the
coil and a frost accumulation correction factor may not need to be
EQUIPMENT SELECTION PROCEDURE
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considered.
When frost does accumulate on the outdoor unit coil, the outdoor
unit capacity is affected and a defrost algorithm will start automati-
cally. The timing between defrost periods is determined by the
system's ability to achieve a target head pressure value. If frost
accumulation is expected to occur at or near the winter design
day conditions, LATS will automatically apply a frost accumulation
factor if the check box labeled "Defrost Factor" in the outdoor unit
selection dialog box is marked. The dialog box can be accessed by
double-clicking on the outdoor unit image. If checked, the corrected
outdoor unit capacity provided by the LATS report and displayed
on the tree mode piping diagram will be automatically adjusted for
outdoor unit coil frost accumulation.
To manually apply the frost accumulation factor, multiply the outdoor
unit's manually calculated heating capacity or corrected heating
capacity reported in LATS (verify the "Defrost Factor" check box was
not marked) by the appropriate frost accumulation factor found in
Table 21.
If the Multi V Mini system will be installed at a significant elevation
above sea level, apply the frost accumulation factor (if necessary) to
the corrected Heating capacity, and then multiply the resultant by the
appropriate altitude correction factor.
After applying the appropriate heating correction factors, verify the
outdoor unit actual corrected heating capacity is at least equal to the
sum of the peak heating loads for all spaces and/or thermal zones
served by the system.
System Sizing Checks
Calculate the Corrected Capacity Ratio (CCR)
The system's CCR is defined as the building total load divided by the
outdoor unit corrected capacity after all applicable correction factors
are applied. Calculate this ratio for both the cooling and heating
design days.
(
Total Cooling Block Load
CCR% =
Actual Corrected Outdoor
(Clg)
Unit Cooling Capacity
(
Heating Peak Load
CCR% =
Actual Corrected Outdoor
(Htg)
Unit Heating Capacity
ARUN 036, 047, 053
x 100 ≤ 100%
x 100 ≤ 100%
53
SYSTEM ENGINEERING
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