Practical research on effective use of simulation for HVAC...

Practical research on effective use of simulation for HVAC systems

in the retro-commissioning process

H. Tanaka1, S. Ito2, Y. Morikawa3, Y. Akashi4, and M. Yamaha5

1 Campus Planning&Environment Management Office, Nagoya University, Nagoya,

464-8603, Japan 2 SANKI Engineering Co., Ltd., Akashicho, Chuo-ku, Tokyo, 104-8506, Japan 3 Kiuchi Construction Co., Ltd., kuniyoshida, Suruga-ku, Shizuoka, 422-8633, Japan 4 Graduate School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku,

Tokyo, 113-8656, Japan 5 College of Engineering, Chubu University, Kasugai, Aichi, 487-8603, Japan

ABSTRACT This paper discusses a method and significance of utilizing simulations for HVAC

systems in a retro-commissioning process. In the retro-commissioning project in this

study, the performance of air-side HVAC systems were verified based on operational data derived from BEMS (Building Energy Management System) and short-term

simple measurements. Also, system simulations were conducted for the air-side

HVAC system with operational data to evaluate the effect of future retrofit. The LCEM tool was used to examine and simulate the effect of reducing the

electricity consumed by fans by replacing air distribution system from CAV to VAV.

The results indicate that VAV retrofitting may cut energy consumption by 52% in summer season, by 62% in winter on the entire typical office floor. The behavior of

air-side HVAC system, and energy performance after retrofit improvement could be

estimated by using system simulation based on actual operational data.

KEYWORDS Retro-commissioning, System simulation, LCEM tool, Operational data, BEMS

INTRODUCTION In the retro-commissioning process, if the actual operational data for HVAC system

is obtained and saved by BEMS and the like, to suggest options for the system

improvement on the ground of this operational data is very important task for the

commissioning team. In addition, system simulation by using the operational data provides more reliable results for the suggestions. The application of this approach,

there are some practical examples for the HVAC heat source system, but the

application example for air-side HVAC system is extremely small. Therefore, the purpose of this study is to show a specific application example.

340

AC-30 AC-30 AC-30 AC-30

AC-30

AC-30

AC-31 AC-30 AC-30 AC-30

Figure 1. Typical floor plan of the building

Table 1. Specifications of AHU ※Air volume and Input in ( ) after adjustment by fan Inverter. AC-

No.

Specifications

Office on north side

Input

kW

AC-

No.

Specifications

Office on south side

Input

kW

301 Capacity： Cooling 44.2kW, Heating 25.6kW

Air volume：7,700m3/h, Fresh air：1,300 m3/h

[VAV]

3.7310

Capacity： Cooling 47.7kW, Heating 25.6kW


[VAV]

3.7

302


Air volume：7,500m3/h (5,338 m3/h)

Fresh air：1,950 m3/h

[CAV]

3.7

(1.2)309


Air volume：7,500m3/h (5,527 m3/h)


[CAV]

3.7

(1.1)


Air volume：7,000m3/h (6,510 m3/h)

[CAV]

3.7

(1.9)308


Air volume：4,000m3/h (1,765 m3/h)

[CAV]

1.5

(0.8)

304


Air volume：7,500m3/h (5,236 m3/h)


[CAV]

3.7

(1.2)307


Air volume：7,500m3/h (5,508 m3/h)


[CAV]

3.7

(1.2)



[VAV]

3.7306



[VAV]

3.7

OUTLINE OF THE SYSTEM The facility that a retro-

commissioning process is applied is

an office building (completed in

1994) with seven floors above ground and about 25,000 m2 total

floor area. Supply heat for cooling/

heating is distributed to this building from an energy plant

within the premises. The building is

air-conditioned by single duct AHU (air handling unit) systems with

VAV (variable air volume) and CAV

(constant air volume) control. Figure 1 and Table 1 show the AHU zoning on the typical floor (the 3rd floor), and

the specifications of the air conditioners. The typical floor has office zones on the

north and south sides. Their interior zones are air-conditioned by two AHUs with CAV control. The perimeter zone on the north and south sides are air-conditioned with

CAV air handlers without fresh air. The perimeter zone on the east and west sides are

air-conditioned with VAV air handlers. In terms of introducing outdoor (fresh) air, respective AHU acquire a constant air volume by means of CAV units.

COMPREHENSION OF THE HVAC SYSTEM OPERATION (1) Overview of simple measurements and evaluation method

During the air-conditioning period (Jul.1–Sep.9, and (Nov.1–Dec27, 2012),

temperature and humidity data for the indoor air and air conditioner outlet/inlet air was obtained by short-term simple measurements and BEMS (Building Energy

Management System) to identify the behavior of the air conditioners. The fan currents

of AHUs on the VAV control were measured in time series.

341

Table 2. Simple measurement point ※○：BEMS data，●：short-term simple measurement

AC No. Room air Temp. Supply air Temp Supply air RH Return air Temp. Return air RH

301, 305, 306, 310 ○ ○ Assumed 90% Room Temp. ○

302, 304, 307, 309 ● ● ○ ○

303, 308 ○ ● ● ○

3600/83.0

SAMASA

c

SA

OAOARARAMA

OASARA

hhV

q

V

hVhVh

VVV

Figure 2. Overview of calculating a heat extraction rate of AHU

The measured currents and manufactural specifications of the characteristics curve

current vs. supply air volume were used to estimate the supply air volume and fan electric power consumption of AHU and to calculate the heat extraction rate of AHU,

etc. The supply air volume of AHU on the CAV control was estimated based on the

current and voltage values (after inverter control), which were checked by spot measurements. Table 2 shows simple measurement points for temperature and

humidity.

(2) Evaluation of the behavior of the air-side HVAC system

Figure 2 shows an overview of calculating the heat extraction rate of AHU using

simple measurement data. V, h, qc are air volume[m3/h], specific enthalpy[kJ/kg] and heat extraction rate of AHU coil [kW], and subscripts SA, MA, RA and OA are supply

air, mixed air, return air and outdoor (fresh) air, respectively, in the figure.

Figure 3 shows examples of analysis results of the heat extraction rate of AHU in cooling/heating season. The amount of heat removed by AC-301 and 308 is very

small throughout the period, partly due to mutual interference with adjacent AHUs.

AC-303 and 308 were mainly used for air circulation even in the main air-conditioning period. One of the options is to stop these AHUs because outside air

is not introduced. The CAV system is subject to large load fluctuations, and is mostly

operated in the heat load range much lower than the rated capacity. This indicates that energy consumption may be significantly reduced by retrofitting to VAV system.

SYSTEM RETOROFITTING SIMULATION (1) Outline of the simulation modeling

LCEM tool Ver. 3.10 (MILT 2014) was used to simulate the effect of reducing the

electricity consumed by fans by retrofitting AHUs (AC-302, 303, 304, 307, 308, and 309) from CAV to VAV. Figure 4 shows an example object of system elements

supplied by LCEM tool and its data flow (Ito 2007 et al.). The object is composed of

“Communication, Control, Method(calculation) and Property(specification)” sections.

hOA hSA

VSA

hMA

hRA

VOA

VRA AHU

Fan

Coil CAV unit

Fresh Air

Return air

Supply air

342

Figure 3-(a). Heat extraction rate of AHU in cooling season

Figure 3-(b). Heat extraction rate of AHU in heating season

Each object exchanges information with only the neighboring objects on both sides. In this process, the objects calculate the output(s) based on an energy balance

calculation. The calculation adopts a static simulation and its time step is one hour.

Regarding the AHU fans, each P-Q characteristic curve (air volume vs static pressure) and motor efficiency are refracted to the fan object. And pressure and power consumption of fan are calculated under supply air volume (B) as shown in Figure 5.

‐100

‐75

‐50

‐25

0

11/1

11/6

11/11

11/16

11/21

11/26

12/1

12/6

12/11

12/16

12/21

12/26

Hea

t ext

ract

ion

rate

of A

HU

（kW

）

0

5

10

11/1

11/6

11/11

11/16

11/21

11/26

12/1

12/6

12/11

12/16

12/21

12/26

Air Volum

e ×1000 (㎥

/h)

0

5

10

11/1

11/6

11/11

11/16

11/21

11/26

12/1

12/6

12/11

12/16

12/21

12/26

Air Volum

e ×1000 (㎥

/h)

‐100

‐75

‐50

‐25

0

11/1

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11/11

11/16

11/21

11/26

12/1

12/6

12/11

12/16

12/21

12/26

Hea

t ext

ract

ion

rate

of A

HU

（kW

）

0

5

10

7/1

7/6

7/11

7/16

7/21

7/26

7/31 8/5

8/10

8/15

8/20

8/25

8/30 9/4

9/9

Air Volum

e ×1000 (㎥

/h)

0

25

50

75

100

7/1

7/6

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7/16

7/21

7/26

7/31

8/5

8/10

8/15

8/20

8/25

8/30

9/4

9/9

Hea

t ext

ract

ion

rate

of A

HU

（kW

)

0

5

10

7/1

7/6

7/11

7/16

7/21

7/26

7/31 8/5

8/10

8/15

8/20

8/25

8/30 9/4

9/9

Air Volum

e ×1000 (㎥

/h)

0

25

50

75

100

7/1

7/6

7/1

1

7/1

6

7/2

1

7/2

6

7/3

1

8/5

8/1

0

8/1

5

8/2

0

8/2

5

8/3

0

9/4

9/9

Hea

t ext

ract

ion

rate

of A

HU

（kW

）

Heat extraction rate of AHU coil [kW] Cooling Capacity [kW] Supply air volume [m3/h] Return air volume [m3/h]

【AC-301：VAV】【AC-302：CAV】

【AC-304：CAV】【AC-308：CAV】

Heat extraction rate of AHU coil [kW] Heating Capacity [kW] Supply air volume [m3/h] Return air volume [m3/h]

【AC-301：VAV】【AC-302：CAV】

【AC-304：CAV】

【AC-308：CAV】

343

Figure 4. Example of Object (Cooling Tower)

Figure 5. The model of fan control

Figure 6. AHU system diagram of LCEM tool

(2) Assumption and boundary condition

In this simulation, it is supposed that each AHU meets the same

thermal load after retrofitting from

CAV to VAV control. In the LCEM tool, objects were connected as

shown in Figure 6 to develop a

modeling of the AHU systems. The cooling/heating water coil

objects used in the simulation were

selected from LCEM tool that are close to actual coil specifications.

The air conditioner fan specific-

ations were checked for the P-Q characteristics of AHU fans, and

were used for the fan modeling. The

minimum supply air volume of AHU was set to each outdoor

(fresh) air volume.

The boundary conditions are as follows: cooling/heating water coil

inlet water temperature: 7°C/45°C,

air supply temperature: 16°C/30°C (based on the actual situation),

outdoor air temperature and relative

humidity: actual measurement values, room heat load: calculation values based on actual measurements, room reference temperature and humidity: actual room

temperature and humidity derived from central monitoring.

The room sensible/latent heat load and room reference temperature and humidity are given as boundary conditions based on actual measurements (room temperature

and humidity, supply air temperature and humidity, and supply air volume). The

outdoor air heat load is added to the coil load calculated by the introduced outdoor air volume and its air temperature and humidity by time of day.

WB Temp. [℃] 16.4 ON/OFF()ON=1, OFF=0) 1 ON/OFF()ON=1, OFF=0) 1

Water Flow Rate ［l/min］ 2,000 Water Flow Rate ［l/min］ 2,000

Outlet Water Temp. ［℃］ 28.0 Supply Cooling W Temp. ［℃］ 28.0

Inlet Water Temp. ［℃］ 37.0 Return Cooling W Temp. ［℃］ 37.0

WB Temp ［℃］ 16.4

Cooling Water SP ［℃］ 28.0

Ratio of Water Flow ［％］ 100

TD Sim ［℃］ 16.4

Fan Powe ［kW］ 1.8

Outlet Water Temp. ［℃］ 28.0

ERROR good

Fan Power DP（kW） 4.0

Water Flow Rate DP ［l/min］ 2,000

Adjustment Paramete a 1.0

Adjustment Paramete b 0.0

SPECIFICATION

Outside Air Cooling Tower Cooling pump

CONTROL

Air Volume [×1000 m3/h]

B: Required Volume

A⇒C :CAV

A⇒D :VAV (P=const.)

A⇒E :VAV (P∝Q2.)

INPUT： INPUT：

　supply water temp. 　fresh air volume

outdoor air condition INPUT：

room heat load

ref. temp.& RH

AC on-off

OUTPUT： OUTPUT： OUTPUT：

　return water temp. 　heat extraction rate 　fan power

　supply water volume 　air state static pressure

supply water

boundary

cooling/heating coil

OBJ

AHU unit(humidifier)

OBJ

fan (supply, return)

OBJ ductOBJ

outdoor airboundary

AHU unit(fresh air)

OBJ

VAV･CAVunitOBJ

roomboundary

344

RESULTS AND DISCUSSION Figure 7 shows the results of retrofitting CAV systems to VAV systems for the

typical office floor, and Figure 8 shows the details of system behavior. Table 3 shows

ATF (Air Transport Factor: indoor sensible heat load/electric power consumption by

fans) calculation results before and after retrofitting, based on actual measurements and simulation results.

The results indicate that VAV retrofitting may cut energy consumption by 52% in

cooling season, by 62% in heating season on the entire typical office floor. ATF was improved more than double from 8 (at present) to 16 in summer, from 5 (at present) to

18 in winter. In particular, a large effect was obtained in winter.

Also note that it is assumed that the operation of AC-303 and 308 are stopped in winter, because heat extraction rate of these AHUs have been almost zero during

heating season in actual operation. Therefore, their ATFs have been hidden in Table 3.

In addition, energy efficiency can be improved by stopping the AC303 and 308, but there is the potential for a negative effect on the indoor air quality and the temperature

distribution.

CONCLUSION AND IMPLICATIONS The behavior and the performance of the air-side HVAC system could be verified

using operation data derived from BEMS and short-term easy measurements.

Table 3. ATF(Air Transport Factor) of AHU Cooling season: Heating season:

AC No. 301 302 303 304 305 306

Actual 7.5 12.8 3.2 1 18.2 21.1

Retrofit 7.5 18.6 18.9 3.4 18.2 21.1

AC No. 307 308 309 310

Actual 6.6 0.5 15.2 17.4

Retrofit 17 39.8 15.9 17.4

entire floor

8

16.2

AC No. 301 302 303 304 305 306

Actual 0.7 10.5 3.6 4.2 3.0 1.4

Retrofit 0.7 17.9 － 12.9 3.0 1.4

AC No. 307 308 309 310

Actual 4.2 11.1 7.0 62.5

Retrofit 11.2 － 15.3 62.5

entire floor

6.4

17.7

※AC301,305,306 and 310 are VAV system already, their ATF is the same value before and after retrofitting

Figure 7. Seasonal electric power consumption of AHU fans

0

5

10

15

20

25

30

1 2

Fan

Pow

er

consu

mpt

ion （

MW

h）

Nov. 1～ Dec. 31

Reduction rate62%

AC301AC302

AC303

AC304AC305

AC306AC307

AC308

AC309AC310

8.49

22.31

0

5

10

15

20

25

30

35

40

45

50

CAV合計 VAV合計

Fan

Pow

er

consu

mpt

ion （

MW

h）

Jul. 1～ Sep. 10

AC301AC302

AC303

AC304

AC305AC306AC307

AC308

AC309

AC310

20.01

40.44

Reduction rate49%

Actual condition Retrofit simulation Actual condition Retrofit simulation

345

AC-302 AC-303

AC-304 AC-308

Figure 8-(a). Room heat load and hourly power consumption of AHU fans in summer

For a VAV system, it can grasp the behavior of system operation such as fluctuation of

supply air volume, heat extraction rate of AHU and so on.

With a view to employing VAV for air-side HVAC systems to improve operations, it was demonstrated that system simulation by using the actual operational data

provides more reliable results for the suggestions of the improvement.

ACKNOWLEDGEMENTS The results of this study, it is part of the outcomes of the research committee for an

applications of commissioning process (Building Services Commissioning Association, BSCA in JAPAN). I gratefully acknowledge helpful discussion with the

committee on several points in this paper.

0

10

20

30

40

50

7/1

7/6

7/11

7/16

7/21

7/26

7/31

8/5

8/10

8/15

8/20

8/25

8/30

9/4

9/9

D.B

. Air te

mp.（

℃）

Return Air R.H. Return Air Temp.

0

20

40

60

80

100

7/1

7/6

7/11

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9/4

9/9

Room

heat

load

（kW

) , R

H（％

）sensible heat latent heat

0

0.5

1

1.5

2

2.5

3

3.5

4

7/1

7/6

7/11

7/16

7/21

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7/31

8/5

8/10

8/15

8/20

8/25

8/30

9/4

9/9

Fan

pow

er

consu

mpt

ion（k

W)

CAV

VAV

0

0.5

1

1.5

2

2.5

3

3.5

4

7/1

7/6

7/11

7/16

7/21

7/26

7/31

8/5

8/10

8/15

8/20

8/25

8/30

9/4

9/9

Fan

pow

er c

onsu

mptio

n（kW

)

rated value

0

10

20

30

40

50

7/1

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7/11

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7/31

8/5

8/10

8/15

8/20

8/25

8/30

9/4

9/9

D.B

. Air te

mp.（

℃）


0

20

40

60

80

100

7/1

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7/16

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7/26

7/31

8/5

8/10

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8/20

8/25

8/30

9/4

9/9

Room

heat

load

（kW

) , R

H（％

）

latent heat sensible heat

0

0.5

1

1.5

2

2.5

3

3.5

4

7/1

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7/31

8/5

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8/15

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Fan power consumption（kW

)

CAV VAV

0

0.5

1

1.5

2

2.5

3

3.5

4

7/1

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9/9

Fan

pow

er c

onsu

mptio

n（kW

)

rated value

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AC-302 AC-303

AC-304 AC-308

Figure 8-(b). Room heat load and hourly power consumption of AHU fans in winter

REFERENCES MILT (Ministry of Land, Infrastructure, Transport and Tourism, Japan), 2014. Life

Cycle Management Tool Ver.3.10 (http://www.mlit.go.jp/gobuild/sesaku_lcem

_lcem.html )

M.Ito, Y.Sugihara et al., Development of HVAC system simulation tool for life cycle

energy management, Part 1: Outline of the developed simulation tool for life cycle energy management, Part 2: Development of component models for HVAC

equipment, Proceedings of Building Simulation 2007, pp.1610-1622, 2007

0

10

20

30

40

50D

.B. A

ir tem

p.（℃

）


0

20

40

60

80

100R

oom

heat

load

（kW

) , R

H（％

）

sensible heat

0

0.5

1

1.5

2

2.5

3

3.5

4

11/1

11/3

11/5

11/7

11/9

11/11

11/13

11/15

11/17

11/19

11/21

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11/25

11/27

11/29

12/1

12/3

12/5

12/7

12/9

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12/13

12/15

12/17

12/19

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12/23

12/25

12/27

Fan

pow

er

consu

mpt

ion（k

W)

CAV VAV

0

0.5

1

1.5

2

2.5

3

3.5

4

11/1

11/3

11/5

11/7

11/9

11/11

11/13

11/15

11/17

11/19

11/21

11/23

11/25

11/27

11/29

12/1

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12/27

Fan

pow

er c

onsu

mptio

n（kW

)

rated value

0

10

20

30

40

50

D.B. A

ir temp.（℃

）


0

20

40

60

80

100

Room

heat

load

（kW

) , R

H（％

）

sensible heat

0

0.5

1

1.5

2

2.5

3

3.5

4

11/1

11/3

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Fan power consumption（kW

)

CAV VAV

0

0.5

1

1.5

2

2.5

3

3.5

4

11/1

11/3

11/5

11/7

11/9

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12/25

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Fan

pow

er c

onsu

mptio

n（kW

)

rated value

347

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