Frequently Asked Questions

A. Temperature of Indoor Venues

Question A1 Why does the University use air-conditioning (AC) rather than natural ventilation?
Answer The temperature and relative humidity (RH) in Hong Kong may vary from 12 oC to 33 oC and from 40% to 99% respectively. Using AC for indoor venues of the University is mainly for hygienic reasons and for human comfort. Certain laboratories, equipment and most computer facilities also require the temperature to be set at a certain range to ensure proper functioning.
Question A2 What are the temperature targets for indoor venues on campus?
Answer Temperature of indoor venues is controlled by the central air-conditioning system. Temperature targets are:

Lecture Theatres 24 - 26 oC
Library 24 - 26 oC
CMC Laboratories 24 - 26 oC
Sport Hall 24 - 26 oC
U-concourse / common area 24 - 26 oC
Building Entrance 24 - 26 oC

Remarks: Temperature targets are subject to review in the light of feedback from students and staff, having proper regard to human comfort and hygienic needs.
Question A3 Why the temperature target of lecture theatres (LTs) is set at 24 - 26 oC?
Answer According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers, the temperature range for human comfort in a particular venue depends in part on the human occupancy rate. For instance, for a room of 10 square metres in size with single occupancy, the optimum temperature target to achieve human comfort is 24 - 26 oC. The University sets temperature targets centrally with regard to the density of human occupancy of a venue as well as the nature of human activity therein, which affects the level of heat generated by body metabolism. As LTs have very high density of human occupancy during classes, the temperature target is set at 24 - 26 oC to facilitate comfort of the majority and to safeguard hygienic conditions.
Question A4 Why some users feel "too cold", while some feel "too hot" in the same venue?
Answer People in the same room can feel significant temperature differences in part due to their metabolic rates, which are affected by their body build, health, food and drink intake, and frequency of regular exercise, etc. It is indeed very hard to find an optimal temperature for everyone in a given location. Given the high density of human occupancy in lecture theatres (LTs) during classes, the temperature target is normally set at 24 - 26 oC to facilitate comfort of the majority users. Users who feel cold may add clothes to suit their need. It is not advisable to raise the temperature target upwards as it may undermine the hygienic condition in the LTs.
Question A5 Why is the temperature set at 24 - 26 oC for building entrance areas?
Answer In summer, when the outdoor ambient temperature is around 30 oC , setting the temperature of the building entrance areas at 24 - 26 oC would facilitate a smooth and comfortable transition from hot ambient to cool building environment (normally set at 23.5 oC ). The 24 - 26 oC temperature zone could also slow down the loss of cooled air from indoor to outdoor due to large temperature difference (30 oC & 23.5 oC ).
Question A6 Why is there no temperature control switches in Lecture Theatres (LTs)?
  1. Optimize system operation - The LTs are equipped with temperature and carbon dioxide sensors. The extent of cooled air supply (air temperature & volume) is controlled by the central system to achieve the intended temperature target.
  2. Minimize human error - as most users tend to forget to turn off or reset the temperature on leaving the LTs.

Remarks: In case of special temperature requirement, users are welcome to request CDO to adjust the AC system settings.
Question A7 Why does the air-conditioning (AC) service stop before the campus closing time?
  1. Maximize energy utilization - When the AC system is shut down, the cooled indoor environment would still be at a comfortable temperature range for some time.
  2. Minimize wastage - If the AC service were shut down exactly at the campus closing time, the cooled environment would still last for some time further, hence incurs energy wastage as a consequence.

Remarks: In case of special needs, users are welcome to contact CDO to adjust AC system settings.
Question A8 Can the relative humidity (RH) be lowered by lowering room temperature?
  1. The central air-conditioning (AC) system can set temperature target but not humidity target. The system does not have the feature of precise humidity control.
  2. When the outdoor ambient air goes through the AC system, certain moisture contents will be removed (about 10%). The RH of the indoor air is hence expected to be around 70% or below.
  3. When the temperature setting of AC equipment is lowered to 16 oC or below however, the RH will be raised to 80% or above as a result. (It is an inherent equipment characteristic).

Remarks: In case of special needs or problem encountered, users are welcome to contact CDO for assistance.