Control of Natural Ventilation: (v. 11/95 Technical Note)

Natural ventilation has the potential to replace or supplement air conditioning, comfort cooling and mechanical ventilation. Whilst there are obvious environmental advantages, there are problems to achieving adequate control as the flow of air must be controlled to limit energy consumption and maximize thermal comfort. This "Technical Note" provides guidance on the application of BMS (Building Management System) controls to natural ventilation. The use of automatic controls is not a panacea for ventilation problems. A vent under occupant control should generally be provided, thus allowing the building occupants to manipulate their own environment. However, the provision of automatic control of air inlet vents and inaccessible air outlet vents results in improved ventilation rates, particularly in the summer, thus enhancing the working environment. Further to this, automatic controls offer the opportunity for night cooling techniques, thus helping to ameliorate daytime heat gains. This publication presents a number of generic control strategies for natural ventilation, mixed-mode ventilation and night cooling, which are used to control this enhanced daytime ventilation and night cooling. Procedures for commissioning and fine-tuning buildings using these strategies are described, together with appropriate control setpoints. An analysis of the costs of buildings utlizing various ventilation types is also provided. The guidance is reinforced with the results of monitoring carried out in three naturally ventilated buildings. A description of the buildings is presented, together with details of the control strategies and the results of monitoring. General conclusions regarding the control strategies and the performance of the ventilation system in each of the buildings is presented. Finally, a description and details of the control strategies of eight further buildings utilizing controlled natural ventilation are presented.

Table of Contents:
Part 1 Introduction: natural ventilation; automatic control - decision to use automatic control, automatic versus manual control. Part 2 Generic control strategies: natural ventilation temperature and CO2 control strategy; pre-cooling control strategy no 1; pre-cooling control strategy no 2; mixed-mode ventilation control strategy. Part 3 Ventilation openings: windows; trickle ventilation; dampers. Part 4 Control technology: actuators - window actuators; damper actuators; smoke control applications for natural ventilation - smoke ventilation hardware; sensors - space temperature sensors, slab temperature sensors, external air temperature sensors, rain sensors, wind direction, wind speed, solar gain, air quality sensors, dust/particulate monitoring/filtering, window/ventilator security sensors. Part 5 Monitored results of three buildings: Durrington Bridge House, Durrington, Sussex; Main Atrium, Chelsea and Westminster Hospital, London - general, atrium control strategy, data analysis; cable and Wireless College, Coventry - data analysis. Part 6 Commissioning/fine-tuning procedures: 12-month fine-tuning procedure. Part 7 Costs: system costs - capital costs, energy costs, maintenance costs.