Graphics Programs Reference
In-Depth Information
heatgaintotheinteriorspace.Themajorityofenergythatistransferredtoa
spaceasheatoccursthroughacombinationofconvectionandradiation.The
coolingloadimmediatelypicksuptheconvectivepartoftheenergytransfer,
and any radiant heat is absorbed into the surrounding space constructions
and interior room finishes.
The radiant heat is then transferred via convection from those surfaces to
the space at a delayed time. Interior loads contribute to both the sensible
heat gain of the space and a latent heat gain that is given off by people's
activity within the space. The latent heat gain contributes to the
instantaneous cooling load of the space, while the sensible heat gain from
internals is absorbed and retransmitted by radiation to the space.
Theengine sumsupthecalculated coolingloadstodetermine atotalcooling
load per each design hour, and it selects the highest load, or peak , for the
design of the air-conditioning system. Note that Revit MEP uses, for the
standard calculation, the hours of 6 a.m. to 6 p.m. for the design day, not
the full 24 hours, and only the months of April through November (October
through May for southern-hemisphere locations), not the full calendar year.
The design day is derived from weather data for the location that you set
during project establishment. Weather data is discussed later in this
chapter.
Heating loads are calculated much the same way. The major differences
are the obvious lower outdoor air temperatures in the heating design day,
ignoring solar heat gains and internal heat gains, and the exclusion of the
thermal storage effect of the building construction. Negative heat gains, or
heat losses , are considered to be instantaneous; therefore, heat transfer is
dealtwithasconductive.Latentheatgainsaretreatedasreplacinganyspace
humidity that has been lost to the outdoor environment.
The worst-case load, as determined by the Revit MEP engine, is based on
the design interior and exterior conditions and loads due to infiltration or
ventilation. Although solar effects are ignored, assuming night or cloudy
winter day operation, Revit does recognize internal heat gain from people,
lights, or miscellaneous equipment to offset the heating load needed. These
additional factors can be edited for spaces, as shown in Figure 8.13 . The
Occupancy and Heat Gain settings and the Electrical Loads settings for
lighting and power can either be specified as <Default> values or edited to
suit a particular space.
 
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