ASHRAE Journal - November 2019 - 18

TECHNICAL FEATURE

45
40
35
30
25
20
15
10
5
0

FIGURE 4 Process load versus PEI for medium office cases (averaged across
climate cases).
5.5
5.0
4.5
4.0
3.5
3.0
2.0
2.5
1.5
1.0
0
20
40
60
80
100
120
140
160
Normalized Process Load (%)

PEI

EUI

FIGURE 3 Process load versus EUI for medium office cases (averaged across
climate cases).

0

20

40

Baseline

60
80
100
120
Normalized Process Load (%)
P1 (50%)

O1 (50%)

140

P2 (25%)

O2 (25%)

C1 (50%)

160

P3 (150%)

Baseline

C2 (25%)

O1 (50%)

P1 (50%)

P2 (25%)

O2 (25%)

P3 (150%)

C1 (50%)

C2 (25%)

TABLE 4 PEI values for medium office cases for all climate zones.
PEI RESULTS

1A

2A

2B

3A

3B

3C

4A

4B

4C

5A

5B

5C

6A

6B

7

8

Baseline

2.7

2.6

2.5

2.5

2.4

2.1

2.6

2.3

2.2

2.8

2.5

2.2

3.2

2.8

3.3

3.8

P1 (50%)

3.6

3.5

3.4

3.5

3.2

2.8

3.7

3.2

3.2

4.2

3.5

3.2

4.9

4.2

4.9

5.8

P2 (25%)

4.7

4.7

4.4

4.7

4.3

3.6

5.2

4.3

4.4

5.9

4.9

4.4

7.1

6.0

6.9

8.4

P3 (150%)

2.3

2.2

2.1

2.1

2.0

1.8

2.1

2.0

1.8

2.2

2.0

1.8

2.5

2.2

2.6

2.9

O1 (50%)

2.7

2.6

2.5

2.5

2.4

2.1

2.6

2.3

2.3

2.8

2.5

2.2

3.3

2.8

3.3

3.8

O2 (25%)

2.6

2.6

2.5

2.5

2.4

2.1

2.6

2.4

2.3

2.9

2.5

2.3

3.3

2.9

3.3

3.9

C1 (50%)

3.4

3.3

3.2

3.3

3.1

2.7

3.2

3.0

2.9

3.5

3.2

2.8

3.9

3.5

5.0

6.0

C2 (25%)

4.2

4.2

4.2

4.3

4.0

3.5

4.3

3.9

3.9

4.5

4.2

3.8

5.1

4.5

7.2

8.7

Figures 3 and 4 present EUI and PEI data utilizing averaged results across all climate zones for the medium
office. At low normalized process load, the PEI increases,
with a higher increase for case P1 versus C1. The PEI associated with Case C1 begins to reflect how well a building
and its subsystems reacts to reduced load demand.
Table 4 represents all PEI data points for the medium
office cases, a good starting point for others looking to use
this data further for benchmarking. Tables 5 and 6 represent means and normalized values, respectively, of
EUI and PEI for all modeling cases by building type
and option. The large office building shows the least
amount of sensitivity to change in process load density.
Workplace environments continue to see increases in
occupant density in open plan configurations to reduce
real estate costs and promote collaboration; the analysis
shows a potential energy benefit to this densification.

Discussion

The analysis was intended to provide data that can be

18

ASHRAE JOURNAL

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N O V E M B E R 2 0 19

further built upon and considered for a large variety
of applications. The results show that there may be an
inherent issue with optimizing energy codes around
fixed process load assumptions, particularly for buildings dominated by lighting and process load heat gain.
Between these two components alone, the total power
density has generally decreased from 4 to 0.75 W/ft2 (43
to 8.1 W/m2) over the past 20 years.
PEI may be used for preliminary design target setting. Assume that a building has an average process load
of 0.5 W/ft2 (5.4 W/m2) over a typical year. This would
equate to a process load EUI of 15 kBtu/yr·ft2 (47.3 kWh/
yr·m2). A building with an PEI of 3.0 would theoretically not be able to have an overall EUI any lower than
45 kBtu/yr·ft2 (142 kWh/yr·m2). This allows modelers to
set realistic targets, before any energy modeling is performed, for a typical building type in a specific ASHRAE
climate zone.
The National Renewable Energy Laboratory has developed useful guidance for evaluating process loads, based
ASHRAE Journal - November 2019

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