AIR CONDITIONING, COOLING & VENTILATION
It’s getting hot out there: time to talk about overheating and beat the heat
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Nicola Rivers, indoor climate specialist at Zehnder Group UK believes it’s time for a different approach to overcoming overheating challenges and suggests the combination of ventilation with active cooling can offer a low carbon solution to overheating issues in residential properties
limate change has led to increasing summer temperatures and Met Office future climate projections, under a high emissions scenario, suggest the
temperature of hot summer days could increase again by between 3.8 and 6.8 degrees C, in future decades. The EU’s climate service revealed in just February this year that for the for the first time, global warming has exceeded the 1.5˚C threshold across an entire year – and experts claim that the global temperature is likely to continue to rise above pre-industrial levels by 2051. This means heatwaves will increase in frequency making this is a modern-day issue that won’t go away. Our recent summers have already been characterised by extremes in the UK’s climate. Temperature records soared beyond 40˚C for the first time and large parts of the country experienced unprecedented discomfort through overheating, causing many to have to flee their homes in search of cooler and safer dwellings. We already know that high temperatures in homes negatively impact people’s lives. It can cause serious problems with sleep as well as heat stress, and present other major health risks such as heat stroke, impaired sleep and in some cases, even premature death. Building design often contributes to
overheating in modern buildings – especially in Urban Heat Islands like London and Manchester. CIBSE has advised that if the issue is not addressed, 4,500 premature deaths per year are expected by 2050.
Building Regulations – Part O
Overheating is a prevalent problem in residential buildings. CIBSE defines residential overheating according to its fixed temperature test as, ‘when the internal temperature threshold of 26°C is surpassed for over 3% of the time’. Exceeding this temperature threshold for extended periods can affect occupant thermal comfort, health and wellbeing as well as productivity. Within the UK Building Regulations, Approved Document Part O provides guidance to building designers on mitigating overheating in residential buildings and reducing these effects. Its prescriptive approach to optimising glazing, solar shading and natural ventilation clearly outlines preferred solutions to keeping a building cool. But problems occur when external factors dictate that passive ventilation can’t be used to control internal temperatures. For
example, if planning dictates that windows cannot be opened, for risk of noise, security or pollution, Part O lists alternative means - from acoustic façade ventilators and mechanical ventilation to mechanical cooling. The predicted effectiveness of these solutions must be modelled in accordance with TM59 to demonstrate compliance with Part O. Traditional methods of combating overheating often rely on air conditioning units, but this approach can have negative effects on indoor air quality (IAQ). By merely recirculating air, these systems can reintroduce potentially harmful particulates such as dust and allergens, compromising occupants’ health and comfort. These systems use a considerable amount of energy and present a concern amid the escalating energy crisis as more and more turn to increased cooling methods in their lives. As they do so, more strain is put on the national grid and the infrastructure can’t cope. But not only do air-cooling systems use a considerable amount of energy, they also run on planet-harming refrigerant gases that are irreversibly bad for the ozone. In fact, the cooling industry accounts for 10% of all global CO2 emissions* through the cooling system technologies that we deploy, contributing even further to global warming. Air conditioning units are also expensive to run and adds another service on top of the standard workings within the building, which doesn’t fare well for those amidst the cost-of-living crisis. They also tend to sit dormant through the winter months when the temperatures fall again. It’s time for a different approach.
The future of residential cooling
Combining ventilation with active cooling can offer a low carbon solution to overheating issues in residential properties and can be designed in conjunction with dynamic thermal modelling. A new study to implement the Passive House standard on Tall Residential Buildings for example, established that cooling requirements can be reduced by up to 40%, due to the building’s enclosure performance being significantly improved.
In most instances, a mechanical ventilation system such as MEV (Central Extract System) or more likely MVHR (Heat Recovery) forms the base of the strategy for overheating. This can then be adapted accordingly to ensure compliance with best practice guidance (CIBSE TM59). But for us, it’s more than just ventilation and cooling but optimising the overall climate within a home to create a comfortable and healthy living environment all year round. The intangible aspects of comfort are based on scientific results from psychometric investigations and show that overheating and poor ventilation have a direct impact on the comfort in our homes. We typically gauge our comfort feeling based on temperature so it’s essential that we control this effectively.
6 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2024
Zehnder’s seven steps to better ventilation and cooling hierarchy consists of stages or options, some of which are complete standalone solutions and others which are combined, to deliver the required level of cooling capacity, including ventilation and humidity control. These range from purge ventilation in the
form of acoustically treated inline extractor fans, radial ducting to reduce noise, leakage and to maintain lower running speeds, and pre-insulated ductwork to ensure continuously insulated air distribution. Ground to air subsoil exchangers also work in conjunction with the MVHR system with sealed ground loops and a water to air heat exchanger to provide pre- heating in the winter and pre-cooling in the summer on the supply/intake air. But our pioneer product to mitigate
overheating and supply effective ventilation into a property is the Zehnder ComfoAir Q600 with ComfoClime that provides a tempered- air solution to meet Part O, providing a ‘fit for purpose’ product across the construction landscape. It can be effortlessly designed into new build specs that face overheating problems; such as floor to ceiling glazed apartments where natural ventilation is impossible due to environmental and noise pollution outside, and dwellings which are without shade to protect them from the sun’s heat.
The ComfoClime system combines heating, cooling, and ventilation in one unit, providing a viable solution to Part O/TM59 across residential, care homes, and student accommodation. It features an innovative reversible air to air heat pump module that can provide both air tempering and space heating, and it uses passive measures to cool the property first before activating the modulating compressor, resulting in a comfortable climate during both warm and cold periods, which is more energy efficient. These approaches fit seamlessly into hundreds of builds - a templated approach for overheating issues that saves on time and cost. The systems can be planned into the spec and rolled out across a development - being installed quickly and efficiently, ensuring reliable planning and delivery. Modern buildings in the UK are being designed and constructed for greater efficiency, sustainability, and decarbonisation in line with the industry-wide net zero approach. But in our efforts to make our buildings tighter, taller and better-insulated, houses and buildings, are at increased risk from overheating and this can’t be ignored.
Right now, over 4 million homes in England
report problems with overheating, and more new builds are set to face these same issues as the call for energy efficiency increases. Building designers need to consider the impact of overheating from initial design stage – designing for the future climate predictions and safeguarding residents against the dangers of forthcoming heatwaves so that they can stay in their homes all year round.
Read the latest at:
www.bsee.co.uk
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