In northern China, there are a large number of space buildings divided in inner zone and exterior zone based on usage requirements. The exterior zone needs to be heated in winter and cooled in summer, while the inner zone needs to be cooled both in winter and summer. Taking a practical project as example, this paper analyzes the energy consumption of a VAV air conditioning system that is shared by inner zone and exterior zone. The paper also points out the serious problem of useless energy consumption for this kind of system

Dongdong, L.

Li, Z.

Ling, C.

Mei, S.

Wenji, G.

Texas A&M University

ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5 
Problem of Vain Energy Consumption in a VAV Air Conditioning System 
Shared By an Inner Zone and Exterior Zone 
Guan Wenji, Cai Ling, Li Dongdong, Song Mei, Zhang Li 
China Architecture Design & Research Group 
Beijing P.R.China 
guanwenji@263.net 
 
Abstract: In northern China, there are a large number 
of space buildings divided in inner zone and exterior 
zone based on usage requirements. The exterior zone 
needs to be heated in winter and cooled in summer, 
while the inner zone needs to be cooled both in winter 
and summer. Taking a practical project as example, this 
paper analyzes the energy consumption of a VAV air 
conditioning system that is shared by inner zone and 
exterior zone. The paper also points out the serious 
problem of useless energy consumption for this kind of 
system. 
Key words: inner and exterior zone, shared by, VAV air 
conditioning system 
 
1．QUESTION PROPOSING 
There are many new office buildings obviously 
can be districted in inner and exterior zone in Beijing. 
The approximately basically horizontal pattern of the 
standard floor is the core in the center, in the core 
there are elevator rooms, stair hall, power distribution 
room, toilet, air conditioning room and various 
pipeline shafts, and out of the core is the office 
districts with long depth of the building. 
From the using function, an office area can not 
be used as one space, which normally is divided into 
several small rooms within the inner and exterior 
zone. For the air-condition system, inner zone is to be 
cooled all the year around and exterior zone is to be 
heated in winter and cooled in summer. This kind of 
building, generally is adopted primary air fan coil 
system or variable air volume air condition system, 
the latter one applied increasing in recent years. 
Primary air fan coil system mostly is made zoning 
two-pipe water systems in inner and exterior zone 
which inner zone is to be cooled all the year around 
and exterior zone is to be heated in winter and cooled 
in summer. When the variable air volume air 
conditioning system is to be adopted, theoretically it 
should be made system in different directions and 
inner and exterior zone. It ensues at any time 
supplying air volume effectively to satisfy with same 
VAV system for rooms. In practical project, it’s very 
difficult to adopt putting four sets air condition 
towards exterior zone and one set air condition 
towards inner zone. Because machine room is too big 
with five sets air condition each floor. 
Currently there are a number of projects with 
one set of VAV system in each floor established in 
Beijing, such as Industrial and Commercial Bank of 
China, Zhongguan Village financial center, Beijing 
B7 buildings and so on. To establish one set of VAV 
system in each floor has many advantages, such as 
saving air condition room space and easily air duct 
installation. But there are still a serious problem that 
huge energy counteraction quantity of inner and 
exterior zone 
 
2. TYPICAL PROJECT ANALYSIS 
Total construction area of a project is 220,000 
m2, four floors underground and 24 floors 
double-towers on the ground, including the 5-23th 
overground floor as a standard floor with 3.9m heigh. 
Single tower air conditioned area 1928 m2 per 
standard floor, in which the inner zone is 1062 m2, 
and the exterior 866 m2. The total area of standard 
floor of inner zone is 40356 m2, which of exterior 
zone is 32908 m2. 
One tower standard floor plane to shown like 
Fig 1. In this project one set of VAV system 
established each floor, serves both inner and exterior 
zone, and exterior zone establishes the radiator for 
heating. Now just analysis the winter conditions, that 
exterior zone be heated, while that of inner one be 
cooled. 
ESL-IC-06-11-117 
Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 
ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5 
 
Fig 1 One tower standard floor plane 
In the design conditions, the minimum supply 
air volume in winter. The air supply volume and fresh 
air volume of the system is constant values. After the 
computation, the air supply volume L＝29190 m3/h 
and fresh air proportion m=39%. The indoor design 
conditions in winter is tN=22, Ф=40%; namely the 
enthalpy value of indoor air iN=39.10 kJ/kg. The 
exterior zone is to be heated, while inner zone is to be 
cooled both in winter. One VAV air conditioning unit 
is shared by inner and exterior zone. The inner zone 
uses single duct variable air volume terminal, and the 
exterior one uses fan powered variable air volume 
terminal. In order to satisfy exterior zone heating 
needs in winter, used the radiator as auxiliary heating 
system. 
For the winter conditions, according to the 
cooling and moisture load calculates out the supply 
air parameter and air volume of inner zone. Because 
the cooling and moisture load of inner zone causes 
only by indoor heating gain (including heat from 
occupant, from lighting and from appliance and 
equipment), which has nothing to do with outdoor 
condition. Therefore, the load of inner zone cooling 
and moisture in winter and which in summer are the 
same. Thus, the supply air parameter and volume of 
inner zone in winter and which in summer are the 
same. After computation, for this project the enthalpy 
value of inner (exterior) zone supply air iS =29.94 
kJ/kg. 
Enthalpy value of mixing air iC 
iC = m × iW + ( 1 – m ) × iN 
iC: enthalpy value of mixing air, kJ/kg 
m: fresh air proportion in winter, in this project 
m=0.39 
iW: enthalpy value of outdoor air, kJ/kg; based on 
outdoor hourly annual value offered by China 
Meteorological Administration 
iN: enthalpy value of indoor air, kJ/kg; in this project 
iN =39.10 kJ/kg 
In order to in achieve the area supply air temperature 
air conditioning unit must process enthalpy difference 
ΔiC-S = iC - iS 
ΔiC-S: in order to in achieve the area supply air 
temperature air conditioning unit must process 
enthalpy difference 
iC: enthalpy value of mixing air, kJ/kg 
iS: enthalpy value of inner (exterior) zone supply air; 
in this project is =29.94 kJ/kg 
    When ΔiC-S＝0, mixing air can be supplied 
without heated or cooled, while exterior zone be 
heated by the radiator. When ΔiC-S<0, mixing air need 
be heated to inner zone supply air temperature ts by 
air conditioning unit, while exterior zone be heated 
by the radiator. When ΔiC-S>0, mixing air needs to be 
cooled to inner zone supply air temperature ts by air 
conditioning unit, while exterior zone needs to be 
heated by the radiator, in this condition, exists energy 
counteraction of inner and exterior zone. 
  When enthalpy value of outdoor air is lower than 
which of indoor air iN(39.10 kJ/kg), is the winter 
conditions. At this time, inner zone must process the 
cold load, and exterior one must process the hot load. 
When outdoor condition enthalpy value iW is higher 
than the room condition enthalpy value iN (39.10 
kJ/kg), is the summer operating mode, this time, both 
zone must process the cold load in, does not have, 
exterior zone cold, the thermal counterbalance 
question. 
In summary, when enthalpy value of outdoor air 
iW is less than which of indoor iN, and enthalpy value 
of mixing air iC is higher than which of inner(exterior) 
zone supply air temperature corresponding mixing 
air’s enthalpy value, the system exists, under this 
conditions, energy counteraction of inner and exterior 
zone. In this project, the corresponding condition is 
enthalpy value of outdoor air 0.3 kJ/kg <iW<39.10 
kJ/kg. 
energy counteraction quantity of inner and exterior 
zone Q 
Q = ΔiC-S × L × ρ ÷ 3600 
Annual energy counteraction quantity of inner and 
exterior zone in winter 
ESL-IC-06-11-117 
Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 
ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5 
W = ΣQ × h 
Q: energy counteraction quantity of inner and 
exterior zone in winter, kW 
L: supply air quantity of exterior zone, m3/h; in this 
project L = 13130m3/h 
ρ: the air density, takes the standard condition one 
ρ=1.2kg/m3 
W: Annual energy counteraction quantity of inner and 
exterior zone in winter, kW 
Because this project is an office building, VAV 
system runs only from 8 o'clock to 18 daily. 
Therefore calculates energy consumption in these 
times only. 
The statistical computation results, energy 
counteraction quantity of inner and exterior zone per 
tower each floor in winter is 135332 kWh, converts 
into area 78 kWh each square meter. 
 
3. CONCLUSION 
We can get the conclusion from the analysis, 
exterior zone with air conditioning area 32908 m2 
loses 62t standard coal in one heating season (to 
count according to each 1t standard coal calorific 
capacity 7000kcal), and simultaneously loses the 
refrigeration electricity to consume 1250,000 
kilowatt-hour (to count according to the COP value is 
4), converts into 1,980,000 Yuan approximately. 
Which equals consumes the 1.9 kg standard coal, 
38.8 kilowatt-hours electricity, each square meter. 
China is a nation with great energy consumption. 
Now saving energy is emphasized in the whole world. 
Excavates the potential from improve protection 
structure and system optimization. But this kind of 
air-conditioning system wastes high quality energy. 
Some people may say China's heating policy is 
charging according to floor space. The consumer 
does not have the economic loss and natural cooling 
source can be used in winter. Has never realized, the 
waste thermal energy company also is Earth's 
resources, and the natural heat sink cannot solve the 
winter- supplying -heat problem completely. So we 
appeal here, VAV system should be separately 
established systems in inner and exterior zones in 
order to avoiding unnecessary waste. 
 
REFERENCES 
[1] Can jinglang. Design of VAV air-conditioning 
system. Beijing: China Architecture & Building 
Press, 1997 (In Chinese) 
[2] Cai ling. Design of VAV air-conditioning system for 
B7 mansion in jingrong street in Beijing. 
Beijing:HVAC, 2004,7 (In Chinese) 
[3] Pan Yungang. Design of air-conditioning system for 
high-rise civil buildings. Beijing: China 
Architecture & Building Press, 1999 (In Chinese)
 
ESL-IC-06-11-117 
Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 


English

Problem of Vain Energy Consumption in a VAV Air Conditioning System Shared By an Inner Zone and Exterior Zone

Texas A&amp;M Repository

ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5 Problem of Vain Energy Consumption in a VAV Air Conditioning System Shared By an Inner Zone and Exterior Zone Guan Wenji, Cai Ling, Li Dongdong, Song Mei, Zhang Li China Architecture Design & Research Group Beijing P.R.China guanwenji@263.net  Abstract: In northern China, there are a large number of space buildings divided in inner zone and exterior zone based on usage requirements. The exterior zone needs to be heated in winter and cooled in summer, while the inner zone needs to be cooled both in winter and summer. Taking a practical project as example, this paper analyzes the energy consumption of a VAV air conditioning system that is shared by inner zone and exterior zone. The paper also points out the serious problem of useless energy consumption for this kind of system. Key words: inner and exterior zone, shared by, VAV air conditioning system  1．QUESTION PROPOSING There are many new office buildings obviously can be districted in inner and exterior zone in Beijing. The approximately basically horizontal pattern of the standard floor is the core in the center, in the core there are elevator rooms, stair hall, power distribution room, toilet, air conditioning room and various pipeline shafts, and out of the core is the office districts with long depth of the building. From the using function, an office area can not be used as one space, which normally is divided into several small rooms within the inner and exterior zone. For the air-condition system, inner zone is to be cooled all the year around and exterior zone is to be heated in winter and cooled in summer. This kind of building, generally is adopted primary air fan coil system or variable air volume air condition system, the latter one applied increasing in recent years. Primary air fan coil system mostly is made zoning two-pipe water systems in inner and exterior zone which inner zone is to be cooled all the year around and exterior zone is to be heated in winter and cooled in summer. When the variable air volume air conditioning system is to be adopted, theoretically it should be made system in different directions and inner and exterior zone. It ensues at any time supplying air volume effectively to satisfy with same VAV system for rooms. In practical project, it’s very difficult to adopt putting four sets air condition towards exterior zone and one set air condition towards inner zone. Because machine room is too big with five sets air condition each floor. Currently there are a number of projects with one set of VAV system in each floor established in Beijing, such as Industrial and Commercial Bank of China, Zhongguan Village financial center, Beijing B7 buildings and so on. To establish one set of VAV system in each floor has many advantages, such as saving air condition room space and easily air duct installation. But there are still a serious problem that huge energy counteraction quantity of inner and exterior zone  2. TYPICAL PROJECT ANALYSIS Total construction area of a project is 220,000 m2, four floors underground and 24 floors double-towers on the ground, including the 5-23th overground floor as a standard floor with 3.9m heigh. Single tower air conditioned area 1928 m2 per standard floor, in which the inner zone is 1062 m2, and the exterior 866 m2. The total area of standard floor of inner zone is 40356 m2, which of exterior zone is 32908 m2. One tower standard floor plane to shown like Fig 1. In this project one set of VAV system established each floor, serves both inner and exterior zone, and exterior zone establishes the radiator for heating. Now just analysis the winter conditions, that exterior zone be heated, while that of inner one be cooled. ESL-IC-06-11-117 Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5  Fig 1 One tower standard floor plane In the design conditions, the minimum supply air volume in winter. The air supply volume and fresh air volume of the system is constant values. After the computation, the air supply volume L＝29190 m3/h and fresh air proportion m=39%. The indoor design conditions in winter is tN=22, Ф=40%; namely the enthalpy value of indoor air iN=39.10 kJ/kg. The exterior zone is to be heated, while inner zone is to be cooled both in winter. One VAV air conditioning unit is shared by inner and exterior zone. The inner zone uses single duct variable air volume terminal, and the exterior one uses fan powered variable air volume terminal. In order to satisfy exterior zone heating needs in winter, used the radiator as auxiliary heating system. For the winter conditions, according to the cooling and moisture load calculates out the supply air parameter and air volume of inner zone. Because the cooling and moisture load of inner zone causes only by indoor heating gain (including heat from occupant, from lighting and from appliance and equipment), which has nothing to do with outdoor condition. Therefore, the load of inner zone cooling and moisture in winter and which in summer are the same. Thus, the supply air parameter and volume of inner zone in winter and which in summer are the same. After computation, for this project the enthalpy value of inner (exterior) zone supply air iS =29.94 kJ/kg. Enthalpy value of mixing air iC iC = m × iW + ( 1 – m ) × iN iC: enthalpy value of mixing air, kJ/kg m: fresh air proportion in winter, in this project m=0.39 iW: enthalpy value of outdoor air, kJ/kg; based on outdoor hourly annual value offered by China Meteorological Administration iN: enthalpy value of indoor air, kJ/kg; in this project iN =39.10 kJ/kg In order to in achieve the area supply air temperature air conditioning unit must process enthalpy difference ΔiC-S = iC - iS ΔiC-S: in order to in achieve the area supply air temperature air conditioning unit must process enthalpy difference iC: enthalpy value of mixing air, kJ/kg iS: enthalpy value of inner (exterior) zone supply air; in this project is =29.94 kJ/kg     When ΔiC-S＝0, mixing air can be supplied without heated or cooled, while exterior zone be heated by the radiator. When ΔiC-S<0, mixing air need be heated to inner zone supply air temperature ts by air conditioning unit, while exterior zone be heated by the radiator. When ΔiC-S>0, mixing air needs to be cooled to inner zone supply air temperature ts by air conditioning unit, while exterior zone needs to be heated by the radiator, in this condition, exists energy counteraction of inner and exterior zone.   When enthalpy value of outdoor air is lower than which of indoor air iN(39.10 kJ/kg), is the winter conditions. At this time, inner zone must process the cold load, and exterior one must process the hot load. When outdoor condition enthalpy value iW is higher than the room condition enthalpy value iN (39.10 kJ/kg), is the summer operating mode, this time, both zone must process the cold load in, does not have, exterior zone cold, the thermal counterbalance question. In summary, when enthalpy value of outdoor air iW is less than which of indoor iN, and enthalpy value of mixing air iC is higher than which of inner(exterior) zone supply air temperature corresponding mixing air’s enthalpy value, the system exists, under this conditions, energy counteraction of inner and exterior zone. In this project, the corresponding condition is enthalpy value of outdoor air 0.3 kJ/kg <iW<39.10 kJ/kg. energy counteraction quantity of inner and exterior zone Q Q = ΔiC-S × L × ρ ÷ 3600 Annual energy counteraction quantity of inner and exterior zone in winter ESL-IC-06-11-117 Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ICEBO2006, Shenzhen, China                          HVAC Technologies for Energy Efficiency, Vol. IV-8-5 W = ΣQ × h Q: energy counteraction quantity of inner and exterior zone in winter, kW L: supply air quantity of exterior zone, m3/h; in this project L = 13130m3/h ρ: the air density, takes the standard condition one ρ=1.2kg/m3 W: Annual energy counteraction quantity of inner and exterior zone in winter, kW Because this project is an office building, VAV system runs only from 8 o'clock to 18 daily. Therefore calculates energy consumption in these times only. The statistical computation results, energy counteraction quantity of inner and exterior zone per tower each floor in winter is 135332 kWh, converts into area 78 kWh each square meter.  3. CONCLUSION We can get the conclusion from the analysis, exterior zone with air conditioning area 32908 m2 loses 62t standard coal in one heating season (to count according to each 1t standard coal calorific capacity 7000kcal), and simultaneously loses the refrigeration electricity to consume 1250,000 kilowatt-hour (to count according to the COP value is 4), converts into 1,980,000 Yuan approximately. Which equals consumes the 1.9 kg standard coal, 38.8 kilowatt-hours electricity, each square meter. China is a nation with great energy consumption. Now saving energy is emphasized in the whole world. Excavates the potential from improve protection structure and system optimization. But this kind of air-conditioning system wastes high quality energy. Some people may say China's heating policy is charging according to floor space. The consumer does not have the economic loss and natural cooling source can be used in winter. Has never realized, the waste thermal energy company also is Earth's resources, and the natural heat sink cannot solve the winter- supplying -heat problem completely. So we appeal here, VAV system should be separately established systems in inner and exterior zones in order to avoiding unnecessary waste.  REFERENCES [1] Can jinglang. Design of VAV air-conditioning system. Beijing: China Architecture & Building Press, 1997 (In Chinese) [2] Cai ling. Design of VAV air-conditioning system for B7 mansion in jingrong street in Beijing. Beijing:HVAC, 2004,7 (In Chinese) [3] Pan Yungang. Design of air-conditioning system for high-rise civil buildings. Beijing: China Architecture & Building Press, 1999 (In Chinese) ESL-IC-06-11-117 Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 

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Problem of Vain Energy Consumption in a VAV Air Conditioning System Shared By an Inner Zone and Exterior Zone

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Problem of Vain Energy Consumption in a VAV Air Conditioning System Shared By an Inner Zone and Exterior Zone

Abstract

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Texas A&M University

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