Chapter-4 Heat Storage and Diversity Factors

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Chapter - 4

Heat Storage and Diversity Factors Cooling load (overestimating)

(underestimating) equipment equipment

(overestimating) Cooling system (oversized) equipment

(original design) (actual) cooling load (reasons) () (storage of heat in the building

structure.)

() peak load (Non-simultaneous occurrence of the peak of the individual loads) peak load diversity

() (Stratification of heat, in some cases.)

Cooling load (data) (procedure)

(actual) cooling load peak total instantaneous heat gain cooling load equipment (air volume rate) chilled water cooling load

Cooling Load Calculations

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System (overall) cooling load equipment control Efficiency operating system

(multi-story) (multi-room application) (flexibility) Air side room load individual room control load pickup

air side room load (storage) diversity overall refrigeration capacity building load

. The Importance of Heating & Cooling Load Calculations air

conditioning Cooling load (installation) (maintenance) ()

Cooling load supply air temperature Supply air flow rate supply air temperature flow rate Cooling load supply air temperature flow rate

.. Too-Large System Cooling load over estimate over sized

() system

() "Short-cycling turning itself on and off repeatedly and running for only a short time. equipment short cycling

() Duct work

() (creating large temperature swings)

() System (wear and tear)

() Humidity control equipment dehumitification AHU cooling coil sensible cooling dehumitification RH control

Chapter-4 Heat Storage and Diversity Factors

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.. Too-Small System Cooling load under estimate under sized

(runs continuously) comfort level (extreme weather) equipment copacity portable equipment

(malfunction) (runs continuously) humidity control

.. Correctly Sized System equipment

-

() optimal efficiency () Indoor temperature overall comfort level

(consistent) () Humidity control

(mold or mildew problems) () (excessive noise) short cycle (over work)

. Storage of Heat in Building

... Stuctures (typical) comfort application instantaneous heat gain (sun)

(lights) (people) (walls) (roof) (glass) (transmission thru) infiltration and ventilation air (machinery) (appliances) (electric calculating machines) Instantaneous heat gain (large portion) radiant heat instantaneous radiant heat gain cooling load

Equipment (solid surface) (absorbed by this surface) instantaneous radiant heat gain cooling load Instantaneous heat gain radiant heat convected heat Convected heat cooling load

Cooling Load Calculations

4-4

Radiant heat convected heat (breakdown) (approximately) Tabel 4-1 Radiant heat and convected heat

Heat Gain Source Radiant Heat Convective Heat Solar, without inside 100% - Blinds Solar, with inside blinds 58% 42% Fluorescent Lights 50% 50% Incandescent Lights 80% 20% People* 40% 20% Transmission 60% 40% Infiltration and Ventilation - 100% Machinery or 20-80% 80-20% Appliances

*The remaining 40% is dissipated as latent load.

Transmission load 100% convective load convective load total load (small part) (simplicity) equipment instantaneous load

machinery appliances load (temperature of the surface) (higher the surface temperature) radiant heat load

- Heat gain and cooling load curves.

Chapter-4 Heat Storage and Diversity Factors

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. Constant Space Temperature and Equipment Operating Periods Radiant heat (walls) (floor) (ceiling)

(solid surface) (strikes) (absorbed) (raising the temperature at the surface of the material)

(material) (air adjacent to the surface) (temperaturedifference) (heat flow) (material) convection (conduct )

convection (heat convected from the surface) instantaneous cooling load Radiant heat (portion) (being stored) (resistance to heat flow into the material) (resistance to heat flow into the air film) (ratio)

(construction materials) (resistance to heat flow into the material is much lower than the air resistance) radiant heat (stored) Radiant heat (process of absorbing)

- Solar heat gain and heat gain from electric lights and the corresponding space cooling loads

Cooling Load Calculations

4-6

for a night shutdown air system.

- Actual cooling load, solar heat gain, west exposure, average construction

Heat gain (highly varying) sharp peak (relatively sharp peak of the instantaneous solar heat gain) Peak solar heat gain (-)

(-) (upper curve) (west exposure) (typical) solar heat gain (lower curve) (average construction application) actual cooling load (space temperature) (constant)

peak heat gain (reduction) 40% Peak load (lags the peak heat gain by approximately 1 hour)

(-) (cross-hatched areas) (heat stored) (stored heat removed from the construction)

(Since all of the heat coming into a space must be removed) (two areas are equal)

(lighting) cooling load (relatively constant) (lights are turned on) (with a decreasing amount being stored the longer the lights are on, as illustrated in.) (-)

(material becomes warmer) (less capable of storing more heat)

Chapter-4 Heat Storage and Diversity Factors

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(-) (upper curve) (fluorescent light) instantaneous heat gain (lower curves) actual cooling load (constant space temperature) (cross-hatched areas) heat stored (dotted line) actual cooling load

- Actual cooling load from fluorescent lights, average construction

(-) (-) (average construction) instantaneous heat gain actual cooling load (relationship) (light construction) (heat) Peak load (storage capacity) (heavy construction) (heat) Peak load (storage capacity)

cooling load cooling load

- Actual cooling load, solar heat gain, light, medium and heavy construction

Cooling Load Calculations

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(-) (upper curve) 30 LB/SQ FT

() instantaneous solar heat gain ()(three lower curves) 100 LB/SQ FT 150 LB/SQ FT (storage of heat) time lag actual cooling load instantaneous solar heat gain ( 150 LB/SQ FT instantaneous solar heat gain

(-) (light construction) (medium construction) (heavy construction) heat gain (curve) (constant temperature in the space) (storage of heat) (significantly affects) air conditioning equipment (operating period)

(-) Pulldonw load, solar heat gain, west exposure, 16-hour operation

(-) (-) (-) curve () air conditioning system actual cooling load

Equipment (turned on the next day)

(heat in must equal heat out) pulldown load (-)

(-) (lighter the building construction, the more attention should be given to zoning.) diversity

Equipment ()(16 hours of operation) (shut down) (some of the stored heat) building construction air conditioning system (heat must be removed)

Chapter-4 Heat Storage and Diversity Factors

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pulldown load Pulldown load cooling load

(-) () () cooling load (cooling load for that day results in the actual cooling load for 16-hour operation)

(-) (upper curve) instantaneous heat gain (lower curve) actual cooling load air con equipment (operating period) space (constant temperature maintained) (doted line) (heat left in the building construction) (additional) cooling load

- Actual cooling load, solar heat gain, west exposure, 16-hour operation

(shutdown period) (night time) transmission load (stored heat) (temperature in the space rises)

- Pulldown load, solar heat gain, west exposure, 12 hours operation

() air con pulldown load Pulldown pulldown periods (brought back to the control point) (pulldown)

Cooling Load Calculations

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pulldown period pulldown load

- Pulldown load, solar heat gain, west exposure, 12 hours operation

(shorter periods of operation) pulldown load air conditioning system (more stored heat is left in the building construction when the equipment is shut off.) (-) pulldown load 12-hour operation