Some of the key factors for improving energy efficiency in relation to indoor applications are the control of Relative Humidity (RH) and temperature. The question is, how to control RH to acceptable levels in an energy efficient manner. Energy efficient humidity control has a very strong bearing on thermal comfort, Indoor Air Quality (IAQ) and eventually on the health and performance of occupants in air-conditioned buildings.
Passivhaus buildings are built to a voluntary standard to improve energy efficiency and reduce ecological footprint.
IAQ control seeks to reduce Volatile Organic Compounds (VOCs), and other air impurities such as microbial contaminants. As such it is important to control relative humidity which can be a key factor leading to mould growth and the presence of bacteria and viruses, dust mites and other such organisms.
Buildings rely on a properly designed ventilation system to provide an adequate supply of cleaner air from outdoors or filtered and recirculated air
Buildings may rely on dehumidifiers like the one above to reduce RH levels to a comfortable range
Air-conditioning systems typically employ a high level of air recirculation to save energy during cooling and dehumidification. Typically recirculation rates are around 80-90%, but can sometimes be even higher. The challenge is not so much in dehumidification, but in doing so without having to overcool. As such, ventilation is integrated for general comfort and economical saving.
Rooms are often designed with specific conditions in mind including temperature, humidity, brightness, noise, and air flow. Careful engineering and implementation of building automation and control is the only way to ensure energy efficiency and building operation conditions are met during occupancy, at the lowest possible costs.
IAQ Facts:
Energy Efficiency (EE) refers to either the reduction of energy inputs for a given service or the enhancement of a service for a given amount of energy inputs.
Relative humidity is highly temperature dependent, so if the temperature is stable, it is much easier to achieve a stable RH.
Air in our atmosphere is a mixture of gases with very large distances between molecules. Therefore, air can accommodate a large quantity of water vapor. The warmer the air, the more water vapor can be accommodated.
Why the need to measure, temperature and relative humidity?
Precise temperature control of air which is supplied to a room results in maximum comfort for the occupants. The temperature should be held constantly at a particular set point to achieve this comfort.
Readings from temperature transmitters installed in the air supply duct are compared to readings inside a particular room. It is easiest to achieve a constant room temperature if there is little difference between the two values. Air temperature control in supply ducts can be employed in rooms in which the air handling unit is used mainly for the renewal of air.
Rotronic manufactures temperature and humidity transmitters such as the one above which are suitable for use in spaces where appearance is a factor.
It is with good RH control that we can process the air for air conditioned rooms independent of the state of outside air and the processes taking place in the room. This way the RH remains constant or within the preset limits and thus energy consumption for humidification and dehumidification is minimized.
Air conditioning is supposed to maintain room temperature and RH as precisely as possible through the use of systems which monitor and control temperature and humidity in the room (or in the air supply ducts to the room). Systems must be dynamic to manage the changing room air quality depending on the occupants and usage.
With precise measurement and control of temperature and humidity, energy consumption for humidification & dehumidification as well as heating and cooling can be reduced leading to energy efficient building operation with lower energy costs and healthier occupants.
Phil Robinson
Rotronic UK
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