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Heating and Air Conditioning I
Principles of Heating, Ventilating and AirConditioning
R.H. Howell, H.J. Sauer, and W.J. Coad
ASHRAE, 2005
basic textbook/reference material
For ME 421
John P. Renie
Adjunct ProfessorSpring 2009
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Chapter 7Nonresidential Load Calculation Heat Gain through Interior Surfaces
Whenever a conditioned space is next to a space at a different
temperatureheat gain
If no heat sources(tbto)5 F
Floor in contact to ground or basementno effect on cooling load
estimate
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Chapter 7Nonresidential Load Calculation Heat Sources in Conditioned Spaces
PeopleSee Table 7-14
Lightingoften the major component of space loadtherefore
accuracy is needed. Different from electrical paper.
Convective portion immediate picked up by A/C system
Radiative is absorbed and re-released by wall, floors, furniture, etc,
after a time lageven when lights have been turned off. Instantaneous rate of heat gain given by
Special allowance factorTable 7-15
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Chapter 7Nonresidential Load Calculation Table 7-14
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Chapter 7Nonresidential Load Calculation Table 7-14
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Chapter 7Nonresidential Load Calculation Table 7-14
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Chapter 7Nonresidential Load Calculation Figure 7-15
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Chapter 7Nonresidential Load Calculation Light Heat Components
Heat to space loadlight heat directly contributing to the spaceheat gain.
Heat to return loadlight heat released into the above-ceiling
cavity picked up by the return air
Return air plenum equations
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Chapter 7Nonresidential Load Calculation Typical Return Air PlenumHeat balance equations
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Chapter 7Nonresidential Load Calculation Other components to heat gain
Power equipmentTable 7-16
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Chapter 7Nonresidential Load Calculation Other components to heat gain
Hooded and unhooded equipmentTable 7-18
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Chapter 7Nonresidential Load Calculation Other components to heat gain
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Chapter 7Nonresidential Load Calculation Other components to heat gain
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Chapter 7Nonresidential Load Calculation Other components to heat gain
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Chapter 7Nonresidential Load Calculation Other components to heat gain
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Chapter 7Nonresidential Load Calculation Other components to heat gain
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Chapter 7Nonresidential Load Calculation Other components to heat gain
Load diversity
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Chapter 7Nonresidential Load Calculation Other components to heat gain
Ventilation and infiltration air
Moisture transfer through permeable building materials
Miscellaneous sources of heat
Temperature rise in fan stream due to fan inefficiency
Temperature rise in fan stream as a consequence of air staic and
velocity pressure Temperature rise from heat generated by motor and drive
inefficiencies
Air leakage into/ out of ducting
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Chapter 7Nonresidential Load Calculation Description of Radiant Time Series
Based on the assumption of steady-periodic conditions (the designdays weather, occupancy, and heat gain coefficients are identical
for those of preceding daysrepeat on a 24 hour cyclical basis.)
Cooling loads must address two time-delay effects
Delay of conductive heat gain through opaque exterior surfaces
Delay of radiative heat gain conversion to cooling loads Overview (see Figure 7-6)
Solar radiationRTS method same as TFM and TETD/TA
Differencescomputation of conductive heat gain, the splitting of all
heat gains into radiant and convective portions, and the conversion of
radiant heat gains into cooling loads.
Time series multiplicationto account for time delaysradiant timefactors and conduction time factors derived from heat balance
equations
Used for comparing the time delay impact of one construction to
another
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Chapter 7Nonresidential Load Calculation Description of Radiant Time Series
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Chapter 7Nonresidential Load Calculation Description of Radiant Time Series
RTS Procedure
After summing to get the cooling load each hour, peak hour to
select equipmentdo this for each design month to find peak.
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Chapter 7Nonresidential Load Calculation Conduction Time Series
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Chapter 7Nonresidential Load Calculation Conduction Time Series - continued
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Chapter 7Nonresidential Load Calculation Conduction Time Factors Table 7-28 (walls) and 7-29 (roofs)
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Chapter 7Nonresidential Load Calculation Conduction Time Factors Table 7-28 (walls) and 7-29 (roofs)
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Chapter 7Nonresidential Load Calculation Thermal Properties Table 7-30
ExampleWall 1made up of F01, F09, F04, I02, F04,G01, F02
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Chapter 7Nonresidential Load Calculation Cooling Load Calculations Using RTS
Instantaneous cooling load is the rate that heat is convected intothe zone air at a given point in time. Complicated by radiative heat
transfer and the time dependency (time lag or dampening) that is
associated. Convective heat gain is immediately a cooling load.
Heat balance procedures in RTS rely on radiative-convective split
to determine contribution of internal loads to the radiative
exchange between surfaces (see Table 7-27)
The radiant time series method converts the radiant portion of
hourly heat gains to hourly cooling loads using radiant time factors,
the coefficients of the radiant time series. Current cooling loads
based on the current and past heat gains.
Two different radiant time series are used Solardirectly transmitted solar heat gainsfloor and furnishing only
Nonsolarall other types of heat gainsuniformly distributed on all
internal surfacesdiffuse solar heat gain and direct solar heat gain
from windows with inside shading
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Chapter 7Nonresidential Load Calculation Cooling Load Calculations Using RTS
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Chapter 7Nonresidential Load Calculation Cooling Load Calculations Using RTS
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Chapter 7Nonresidential Load Calculation Cooling Load Calculations Using RTs
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Chapter 7Nonresidential Load Calculation Cooling Load Calculations Using RTS
Improved accuracy and less subjective inputs
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Chapter 7Nonresidential Load Calculation Heating Load Calculations
Same except ... Credit for solar or internal heat gains not included
Thermal storage of building structure ignored
Worst case load based upon
Design interior and exterior conditions
Infiltration and/or ventilation
No solar effect
No heat gain from lights, people and appliances
Account taken for night-time setback