ASHRAE Journal - November 2020 - 16

TECHNICAL FEATURE

TABLE 2 Zone airflow rates and reheat when single-duct VAV system is used.
A. SINGLE-VAV SYSTEM WITH SAT CONSTANT AT 55°F
CASE

SOUTH (ZONE 1)

Airflow
(cfm)

Airflow
(cfm)

CORE (ZONE 3)

EAST (ZONE 2)

Reheat
(Btu/h)

Airflow
(cfm)

Airflow
(cfm)

WEST (ZONE 4)

Reheat
(Btu/h)

Airflow
(cfm)

Airflow Reheat
(cfm) (Btu/h)

Airflow
(cfm)

Airflow
(cfm)

NORTH (ZONE 5)

Reheat
(Btu/h)

Airflow
(cfm)

Airflow
(cfm)

Reheat
(Btu/h)

1

1,151.9

0

1,000.0

-5,545.5

3,635.2

0

1,000.0

-25,180.1

800.0

-18,703.3

2

1,000.0

-10,827.0

1,355.7

0

3,752.0

0

1,000.0

-22,494.8

800.0

-15,027.8

3

1,000.0

-7,715.2

1,000.0

-7,561.6

4,605.0

0

1,000.0

-7,799.3

800.0

-3,163.0

4

1,823.4

0

2,057.1

0

4,676.5

0

1,000.0

-3,794.9

852.3

0

5

1,865.5

0

1,630.8

0

6,083.5

0

2,887.1

0

1,628.6

0

B. SINGLE-VAV SYSTEM WITH SAT RESET STRATEGY
CASE

SOUTH (ZONE 1)

Airflow
(cfm)

Airflow
(cfm)

EAST (ZONE 2)

Reheat
(Btu/h)

Airflow
(cfm)

Airflow
(cfm)

CORE (ZONE 3)

Reheat
(Btu/h)

WEST (ZONE 4)

Airflow
(cfm)

Airflow Reheat
(cfm) (Btu/h)

Airflow
(cfm)

Airflow
(cfm)

NORTH (ZONE 5)

Reheat
(Btu/h)

Airflow
(cfm)

Airflow
(cfm)

Reheat
(Btu/h)

1

2,303.9

0

1,495.9

0

7,270.5

0

1,000.0

-14,180.1

800.0

-9,903.3

2

1,015.7

0

2,711.4

0

7,504.1

0

1,000.0

-11,494.8

800.0

-6,227.8

3

1,000.0

-2,581.9

1,000.0

-2,428.3

6,006.6

0

1,000.0

-2,666.0

855.9

0

4

1,823.4

0

2,057.1

0

4,676.5

0

1,000.0

-3,794.9

852.3

0

5

1,865.5

0

1,630.8

0

6,083.5

0

2,887.1

0

1,628.6

0

TABLE 3 System-level results when single-duct VAV system is used.
A. SINGLE-VAV SYSTEM WITH SAT CONSTANT AT 55°F
CASE

AIRFLOW (CFM)

AHU1

AHU2

TEMPERATURE (°F)

VENTILATION

OA
AHU1
Required OA (cfm)
(cfm)

OA
AHU2
(cfm)

OAF
AHU1
(%)

OAF
AHU2
(%)

MAT
AHU1

MAT
AHU2

SAT
AHU1

SAT
AHU2

LOADS (BTU/H)

Total
Cooling

Sensible
Cooling

System
Heating Total Reheat

1

7,587.2

2,370.5

4,101.2

54.1

55.0

55.0

0

0

0

-49,428.8

2

7,907.7

2,369.0

4,651.6

58.8

55.0

55.0

0

0

0

-48,349.5

3

8,405.0

2,236.9

8,405.0

100.0

58.0

55.0

27,736.7

27,736.7

0

-26,239.1

4

10,409.2

2,345.7

10,409.2

100.0

67.0

55.0

137,401.7

137,401.7

0

-3,794.9

5

14,095.6

2,305.9

2,305.9

16.4

76.1

55.0

343,141.7

327,858.3

0

0

B. SINGLE-VAV SYSTEM WITH SAT RESET STRATEGY
CASE

AIRFLOW (CFM)

AHU1

AHU2

VENTILATION

OA
AHU1
Required OA (cfm)
(cfm)

OA
AHU2
(cfm)

OAF
AHU1
(%)

OAF
AHU2
(%)

MAT
AHU1

MAT
AHU2

SAT
AHU1

SAT
AHU2

LOADS (BTU/H)

Total
Cooling

Sensible
Cooling

System
Heating Total Reheat

1

12,870.2

2,267.7

3,478.4

27.0

65.0

65.0

0

0

0

-24,083.3

2

13,031.2

2,272.7

3,832.7

29.4

65.0

65.0

0

0

0

-17,722.5

3

9,862.5

2,161.1

8,895.6

90.2

59.7

59.7

0

0

0

-7,676.1

4

10,409.2

2,345.7

10,409.2

100.0

67.0

55.0

137,401.7

137,401.7

0

-3,794.9

5

14,095.6

2,305.9

2,305.9

16.4

76.1

55.0

343,141.7

327,858.3

0

0

air fraction (OAF) is 100%. The outdoor air introduced
is 8,405 cfm (3967 L/s), greater than the ventilation
requirement of 2,237 cfm (1056 L/s). When the supply
air temperature is constant at 55°F (12.7°C), the cooling coil should cool the supply air from 58°F to 55°F
16

TEMPERATURE (°F)

ASHRAE JOURNAL

ashrae.org

N OVEM BER 2020

(14.4 to 12.7°C); this is only sensible load. Core (Zone 3)
needs cooling, and other zones having relatively low
cooling loads need heating, as the SAT of 55°F (12.7°C)
is too cold to maintain the space temperature at 75°F
(12.7°C).
https://www.ashrae.org/
ASHRAE Journal - November 2020

Table of Contents for the Digital Edition of ASHRAE Journal - November 2020
