Overheating in domestic properties is becoming a serious – and largely unexpected – issue. Whole house mechanical ventilation systems provide one means of addressing this, but only if the resident is on side. Jon Hill, Technical Manager of Polypipe Ventilation, offers advice on how to achieve this.
If you are in anyway involved in the domestic ventilation market, you’ve probably noticed a spate of national news stories addressing the issue of overheating in new builds. It seems we have succeeded in insulating and draught proofing our new properties to such an extent that many have become uncomfortably stuffy or hot to live in, especially during the summer periods. With 2015 being one of the warmest years on record, reportedly attributable to global warming, this problem is only set to worsen.
The Zero Carbon Hub, a non-profit organisation supporting the mainstream delivery of low and zero carbon homes in England, published ‘Overheating in Homes – The Big Picture’ in 2015. The report states, “as we get better at building and retrofitting homes to prevent heat losses in the winter, we may inadvertently increase the risk of overheating in warmer months.” It also estimates that up to 20% of the housing stock in England experiences overheating.
Why not just open the windows? I hear you cry. It sounds by far, the most sensible solution.
Why its a problem, especially in highly populated areas
The problem with that eminently rational approach is that occupants are sometimes unable to open their windows wide enough or the windows are too small to make much difference to the temperature inside. Furthermore, some people are actually unwilling to open their windows for the sufficient time required to allow the heat to dissipate due to security, pollution and noise concerns, especially at night. Put yourself in the context of a ground floor apartment in a city next to a busy road; understandably many people would not want to leave their window open, especially not at night. The issue of overheating in highly populated areas, especially within apartment living, is becoming an increasingly important issue; causing many ventilation manufacturers to consider how they can provide solutions to reduce overheating in residential applications.
Ventilation solutions
This is where whole house mechanically driven ventilation has a key role to play, with systems such as Mechanical Extract Ventilation (MEV) or Mechanical Ventilation with Heat Recovery (MVHR). MEV units are designed to continuously extract waste air from a dwelling, to improve the indoor air quality and help prevent condensation and mould from developing. MVHR is seen as more advanced, as it combines mechanical extract ventilation with heat recovery. The extracted air is filtered and passed across a heat exchanger to transfer the otherwise wasted heat to the fresh, filtered supply air, which is consequently pre-warmed and then distributed to the living areas of a dwelling.– ideal for the cooler months. During the summer months however, a 100% bypass function will prevent the energy transfer and instead, the continuous supply of fresh, clean air will help aid the occupants comfort levels.
What to consider when selecting a ventilation system
Nevertheless, just fitting a mechanical ventilation system isn’t enough if the resident is to truly benefit from it. Firstly, they have to understand the principle behind the system; secondly they need to be able to use it easily and have control of the settings to adjust the system to their particular property and satisfy their comfort preferences. Thirdly, the system mustn’t be a nuisance to the resident, otherwise it is likely to be switched off or ignored and not maintained.
MEV and MVHR systems are increasingly being installed into new domestic properties. As a cost-effective means of lowering Dwelling Emission Rates to gain points towards achieving a higher SAP rating (as listed in the Product Characteristics Database), many developers and specifiers are seeing the benefit of adopting a whole house ventilation system, whilst also being able to improve the indoor environment for their clients.
It is however very easy to forget that the vast majority of people in this country have never heard of an MEV or MVHR system before; they don’t know what they are or how they operate. In some cases, they don’t know they even have one in their own home, as the unit may be hidden away in the loft!
To overcome this first hurdle, look to use systems that can be fitted in an easy--access cupboard or a utility room; this also makes it more straightforward to regularly maintain an MVHR unit’s filters. Also, most importantly, the system itself must be easy to operate and where possible the instructions should be attached to the unit permanently, rather than as a separate instruction leaflet which may get lost over time.
Variables that impact the indoor air climate
When it comes to looking at variables that may impact overheating in the home, not all properties are the same. Properties, just like people, come in all shapes and sizes. There are different design styles, different fabrics, different locations and orientations and different heating methods – the list is a long one. As a result, the thermal efficiencies of properties vary wildly. The people living in those properties, their activities and comfort levels all widely vary as well - one person’s comfortable temperature is another’s tropics!
Advanced control
There is, therefore, a very real need for more advanced ventilation systems that put residents in greater control over their indoor environment, enabling them to directly manage the humidity and ambient air temperature of their dwelling.
It’s a balancing act as you don’t want the system’s effectiveness compromised. The simplest solution, I believe, is to provide the resident with a ‘purge’ facility. By this, I mean the ability to boost the air flow through the MVHR system, whether this be by automatic humidity level sensing, by pre-programmed time control or through manually using an external switch. By boosting the air flow, this will allow residents to quickly remove excess humidity and temperature when it becomes noticeably warm or unpleasant.
The other important thing is to make sure the MVHR system has a 100% summer bypass facility, to stop the unit from supplying pre-warmed air into the home during the summer and possibly night time periods. Opting for more advanced models which allow for automated bypass control by room temperature sensing or programmed time settings enables residents to set their own preferences depending on what they consider to be a comfortable indoor air environment.
For convenience, this control should be a separate unit – not part of the MVHR unit – so it can be accessed readily.
New Bluerbrain MVHR control
Polypipe Ventilation offer an intelligent wall mounted controller – the Bluebrain. Through advanced AMIE (Air Management for Indoor Environments) technology, the Bluebrain controller includes features such as digital humidity control, automated summer bypass and accurate system balancing.
Unlike conventional humidity sensors, the Bluebrain control, alongside Polypipe Ventilation’s new MVHR HRX-aQ units, enable occupants to have direct control over managing the humidity levels in their home to suit personal comfort levels. By accurately measuring air humidity, the HRX-aQ’s extract speed automatically changes from background to boost as the level of humidity increases, thereby providing optimal ventilation performance
Reducing sound for a quieter system
Lastly, I would like to look at user acceptance and the issue of noise. A good MVHR and ducting system that has been installed correctly shouldn’t cause unnecessary noise, but there is potential for sound to travel down the ducting from the fan, or from traffic noise if located close to busy roads and even from room-to-room-cross talk. It would therefore be sensible to include duct sound attenuators, which effectively absorb sound over a range of audible frequencies.
Incorporating rigid duct sound attenuators into a whole house system is not only beneficial for home occupants but also helps installers and developers meet Building Regulation recommendations, which advise the system should not produce excessive noise as this may lead to the user adjusting the system detrimentally.
In the case of Polypipe’s own Domus duct sound attenuators, these have been manufactured with Microban® protected foam to protect against microbial growth for a clean and fresh ventilation system. Something the homeowner may well thank you for in a few years’ time and can reduce noise levels by up to 55dB, helping to provide a much quieter system.
Overheating in our homes is a genuine problem. There are currently approximately 2,000 heat-related deaths per year in England and Wales, and this figure is projected to rise to over 7,000 by 2050 as a result of climate change and a growing and ageing population. Balancing the need for well insulated homes that require less heating in colder months to prevent cold related deaths and reduce energy consumption, with a property that is comfortable and safe to live in during the summer is an issue that few of us foresaw. Mechanical ventilation systems that residents understand and can control to meet their personal preferences and circumstances are a step forward in addressing this.
Polypipe Ventilation is a market leading manufacturer and designer of domestic ventilation systems. For more information, please call 03443 715523.