By Kira Jopp on Wed 31 March 2021
What is overheating?
The term overheating refers to the build-up of heat within a building which can lead to discomfort for the occupants.
The World Health Organizations’ guidance on thermal comfort states that temperatures above 24°C cause discomfort, and in the more fragile and susceptible members of the population, can cause harm. CIBSE note that exposure to indoor operative temperatures over 28°C for long periods will result in increased dissatisfaction and reduced productivity in the workplace.
As the temperature rises it triggers the body’s defence mechanisms (such as sweating) then increasing cardiovascular strain and trauma that can lead to heat exhaustion, heatstroke and hospitalisation.
Due to the loss of moisture from sweating, dehydration can also be a problem, particularly for the elderly and the very young.
The likelihood of overheating is dependent upon a number of factors, not least bad building design, poor management or inadequate services. For domestic dwellings, a rural or urban location, the orientation, type of glazing, design and construction materials are all contributory factors.
Causes of overheating:
1. Solar gains through the building fabric.
Heat transmitted through elements of the building fabric include structural materials, cladding, insulation and finishes. While passive solar gains can maximize the use of heat energy from the sun, it can cause overheating.
2. Solar gains through windows.
Direct solar gain through the building glazing may be reflected back through the window from blinds or curtains. However, these elements will eventually be heated and therefore heat the air in the room.
If there are no blinds or curtains, or if they are open, the heat will be absorbed in the dwelling.
3. High external air temperature.
If the temperature outside it higher than it is inside, then any air brought in by ventilation will increase the temperature of the air in the building.
4. Internal heat gains.
Activities that take place throughout a building generates heat such as cooking or bathing in domestic dwellings, and the use of electronic devices or industrial machinery in commercial premises.
Can Airflow Provide any preventative measure to overheating?
Mechanical Ventilation with Heat Recovery (MVHR) systems are becoming more common in both commercial and domestic spaces. These systems recover heat from the exhaust air and return it to the building or dwelling by raising the temperature of the supply air. During colder months this can significantly reduce heating loads, while many of Airflow’s MVHR solutions have a summer by-pass feature which switches off the recovery of heat from the air during summer when buildings are most at risk from overheating.
- Airflow’s Duplexvent and Adroit MVHR units come with 100% automatic summer bypass as standard which ensures the ventilation unit will provide a form of free cooling in the summertime. This process works by shutting off the heat recovery core, filtered fresh air is then provided directly into the building without being heated up, thus giving a cooling effect. Without this bypass facility in place, an MVHR unit can overheat and subsequently cause the building itself to overheat.
- The Duplexvent MVHR units come with an option of either a CHW (Chilled Water) Cooling Coil or a DX (Direct Expansion) Cooling Coil. These coils can either be built-in to the Duplexvent units themselves or bolted on as a retrofit option. Having a cooling coil in place will enable the user to comfort cool the building, with the ability to adjust the temperatures accordingly using a touch screen user interface or via a BMS system.
- DX Direct Expansion cooling coils use a refrigerant. The most commonly used refrigerant in the industry is R410a, however others are available. The DX Coils would connect and work with an external condenser unit which would be located outside of the building, usually on a rooftop or mounted on an external wall.