Control of Distributed Cooling and Ventilation Systems in Hot and Humid Climates

In the research project 3for2 Beyond Efficiency, low-exergy distributed cooling and ventilation systems for application in the tropics are designed and tested in a demonstrator building in Singapore. The HVAC system designed consists of passive chilled beams for sensible cooling, fan coil units for latent cooling and dedicated outdoor air handling systems for IAQ control. The design reduces building space requirements due to less ventilation equipment. Optimally, this may allow building 3 floors in the conventional space of 2 with equal occupant floor-to-ceiling heights, hence the name 3for2. In addition, it proposes to improve comfort of occupants and increase overall building energy efficiency by a factor of two. The demonstration site is a 550 m2 test case of the 3for2 concept in the administrative offices of United World College South East Asia (UWCSEA), an international school in Singapore. The demonstration building was commissioned by end of 2015 and has been running in regular operation since beginning of 2016. 
This paper reports on the basic control strategy implemented and on key elements of the building control. A simulation model representing one zone of the demonstrator building including its control is presented and calibration results using measured data are given. In a simulation case study using the calibrated model, results for two selected building locations (Singapore and New Orleans) were produced. The cases contain different control strategies, different comfort settings as well as different HVAC systems including a conventional air-based only system. These cases allow assessing the benefit of advanced control, but also put it into context by comparison to cases with different comfort requirements or HVAC systems. All cases were assessed based on comfort and electrical energy consumption for HVAC operation. 
In practical application, the implemented control strategy has been able to successfully achieve a high comfort level in an energy efficient way. In simulations, results show that electrical energy use for HVAC varies strongly for the different cases – for the Singapore location from 26% lower to 38% higher than base case – while for most cases comfort settings can be achieved tightly. The simulations indicate that presence detectors and in particular IAQ measurements allow for substantial increase in terms of energy efficiency while still maintaining comfort settings. In hot and humid climates such as in Singapore, morning start-up dehumidification and cooling causes a significant part of whole HVAC energy consumption. Optimized start-up cases are shown to contribute significantly to an energy efficient operation. Both experience from demonstrator operation as well as simulation results substantiate that control is particularly important for the investigated HVAC system since the different subsystems for cooling, dehumidification and IAQ control have to be coordinated in order to achieve the desired performance.