Load Calcs

Question 1

Space Cooling Loads

Answer 1

Building Envelope Loads (heat gain gain thru windows, walls, roofs, etc.) and Internal Loads (people, lighting, & equipment)

Question 2

System Loads

Answer 2

Fan heat gain (from fan & motor), plenum heat gain (from RA) and ventilation load (cooling load from warmer OSA)

Question 3

Cooling Coil Load

Answer 3

Is the summation of space cooling loads, internal loads and system loads

Question 4

Heating Loads

Answer 4

Heat loss that occurs from building envelope loads, ventilation air and infiltration of unwanted OSA. Credits for internal and solar gains are NOT accounted for. Normally assumed as worst case condition and all gains are ZERO.

Question 5

Design Day

Answer 5

The “worst case” day for your air conditioning loads. The “worst case” hour of this day determines equipment capacity, fan sizes, and subsequently duct sizes.

Question 6

Comfort zones for most commercial Bldgs.

Answer 6

Heating setpoint from 68 to 70°F

Cooling setpoint from 73 to 75°F

Question 7

Wet Bulb

Answer 7

Moisture content in the air

Question 8

What is a Zone?

Answer 8

spaces with thermostatic controls and can be a single space or a group of similar spaces.

Question 9

Zoning General Rules

Answer 9

1) Perimeter spaces zoned separately (10-15 for open office perimeter)
2) Perimeter spaces with different exposures are zoned separately.
3) Corner rooms have their own zone
4) Large assembly spaces have their own zone)
5) 4-5 similar enclosed office spaces can be combined

Question 10

U-Value

Answer 10

Describes the ability of a building material to conduct/transfer heat. Takes the entire assembly into account. It’s the reciprocal of R-value that measures the materials resistance to heat.

Question 11

U-Value

Answer 11

Describes the ability of a building material to transfer heat. Takes the entire assembly into account. It’s the reciprocal of R-value that measures the materials resistance to heat.

Question 12

SC

Answer 12

Shading coefficient. Given to us by glazing manufacturer. Measures the amount of solar heat gain through glass relative to a 1/8” clear pane. Values range from 0 (black/opaque) and 1 (clear)

Question 13

SHGC

Answer 13

Solar heat gain coefficient is a fraction of the radiation that enters the building thru glazing. It’s what we feel.

Question 14

Usage Diversity

Answer 14

Plug loads/Electric Loads are generally 50% less than nameplate value due to usage diversity.

Question 15

Where to find common misc. eq loads

Answer 15

ASHRAE Fundamentals Handbook.

Question 16

Where to find common misc. EQ loads

Answer 16

ASHRAE Fundamentals Handbook.

Question 17

How much cfm per person/sq.ft. is required

Answer 17

15 cfm

Question 18

How much cfm per person/sq. ft. is required

Answer 18

15 cfm

Question 19

Peak Load / Peak Zone Load

Answer 19

Used to size HVAC equipment at zone level. Think VAV boxes, FCUs, or heat pumps.

Question 20

System Block Loads

Answer 20

Is based on when the peak occurs for all zones combined. Will always be less than or equal to the sum of peak loads.

Question 21

Why is the system block load not the summation of all peak zone loads?

Answer 21

Peak zone loads may not all occur at the same time. An example would be zones with different solar exposures.

Question 22

Safety factor

Answer 22

Provides spare capacity for central systems. Typically 0-10% for cooling and air systems and 10-30% for heating systems. Only used once in calculation. Not at zone level or in assumptions.