Mechanical intervention

Mechanical intervention

In recent years, a huge amount of research and development has gone into refining mechanical ventilation with heat recovery systems. Tunca Sekban looks at the transformation of MVHR and explains how the industry is beginning to make dramatic changes to ventilation technology and functionality.
Over the last few years, the UK construction industry has taken a positive step towards increasing its focus on building airtight homes to save energy, using insulation to provide maximum warmth in winter and to keep properties cool during the summer months.
However, creating a sealed envelope raises the question of adequate ventilation. Whereas ventilation used to mean simply opening a window, it now signifies something far more complex including how to expel air, prevent damp and mould, and maintain a healthy indoor environment for the occupants. Everyday activities such as cooking, drying laundry and showering all heighten the issue of moisture building up in the air. Therefore, it’s vital that installers think carefully about the best way to remove this moisture – and potentially wasted heat – without compromising the fabric of the building.
Many installers are aware of the existence of ventilation systems, but not all of them will be up to speed with the latest technological advancements.
Mechanical Ventilation with Heat Recovery (MVHR) systems, for example, are increasingly being used in new build housing projects. In fact, the Passive House standard generally requires the installation of an MVHR unit to meet strict dwelling design airflow leakage rate levels – typically under 1.5m3/hr/m2.
The system works by pulling warm, moist air from wet rooms like the kitchen, utility room and bathroom  (would have been otherwise expelled into the environment) and extracts the heat through an exchanger, using it to warm fresh, filtered air being pulled in. The warmed air is then distributed to the living areas and bedrooms. This ventilation and heating system also uses minimal energy by incorporating high efficiency EC motors.
The increasing number of energy efficiency regulations, along with the demand for lower carbon technologies, has resulted in a shift from traditional extract ventilation to a solutions approach in recent times, specifically signifying a rise in the adoption of MVHR and Demand Control Ventilation (DCV).
Other developments include the introduction of a range of sophisticated controls options, along with AC motors being replaced with DC and EC motors, which use less energy and last longer. With lower operating system costs, payback periods have been dramatically reduced.
MVHR units are now more readily available for both residential and commercial projects, with products that offer over 90% heat recovery efficiency with exceptionally low running costs – in certain cases, as little as £9 a month.
When it comes to heat/energy recovery, the plate heat exchanger core is the crucial component to ensure high efficiencies and peak performance. Currently, there are two main types of heat exchanger design – low efficiency and high efficiency. Lower efficiency models use a ‘cross flow’ heat exchanger cell, which is generally square in section and transfers heat from one air flow to another as they pass each other inside the core. These products reach a peak efficiency value of 55-60%.
On the other hand, there has been a shift towards high efficiency models that already meet the 2015 ErP legislation. This has been achieved by using a ‘counter flow’ heat exchanger design that is perfect for applications with restricted space.
Although ‘counter flow’ heat exchangers use similar design principles to ‘cross flow’ versions, they have longer parallel air paths to increase the contact time between air streams, which help deliver a greater heat recovery capacity. Consequently, peak efficiencies of 90-95% can be frequently achieved, particularly as the technology is less sensitive to both air temperature and flow rate fluctuations.
One such development is Airflow’s Duplexvent Flexi, designed to provide comfort ventilation to larger applications such as schools, offices, restaurants, and hotels. Duplexvent Flexi also comes from a product range that contains the only Passive House certified commercial MVHR units currently available in the UK. The system is able to recover up to 95% of the heat that would otherwise be lost, reduce heating costs and ease environmental pressures while improving indoor air quality with F7/F5 high-grade filters.
The unit’s multipurpose design also allows it to be positioned either in a left or right hand configuration with interchangeable spigots to the ducting, providing installers with an easy and convenient method of installation. The unit also has compact ventilators comprising of two high-efficiency EC fans that ensure long life and the lowest possible energy usage, playing a significant role in reducing the energy consumption of the unit and the overall carbon footprint of the building.
Furthermore, a much greater emphasis has been placed on education in the MVHR sector to ensure that installers are not only specifying the right system for a property, but also installing it correctly. This applies to both the unit and the ducting as many reported issues of loss of suction and noise come from poorly connected ductwork.
The latest MVHR systems are also becoming progressively suited to retrofit scenarios in order to increase the overall efficiency of older buildings. Here, ducting has an important role to play, as semi-rigid ducting is now often used in older properties.
A good example of product refinement, suitable for residential dwellings, comes in the form of Airflow Developments’ Airflex Pro ducting. Classed as semi-rigid ducting. It has a unique hydraulic design allowing for interchangeable duct profiles (75mm round to 51mm oval) without any performance loss. It is SAP Appendix Q eligible and also has a high crushability factor of 16 kN/m2, which means air flow can be maintained even through the smallest of spaces – metal web and concrete screeds, narrow gaps and down cavity walls – quickly and easily, saving up to 70% on installation time.
When you consider that the average adult requires 15,000 litres of air every day, and that an average household contains two or more people or a typical office holds teams upward of 10 or more people, the importance of supplying and extracting air becomes very apparent.
Today’s MVHR systems are undergoing a complete overhaul through stringent testing and are providing unprecedented new levels of ventilation to both businesses and homeowners.
More changes to Building Regulations are coming in 2014 and there is an increasing global demand to lower carbon emissions by 2020, but installers who ask the right questions and are aware of what is currently on the market can rest assured that choosing MVHR as a ventilation option will provide a healthy indoor environment to any building.
So for specifiers and building services designers, there are some key pieces of information to look out for when calculating a building’s ventilation requirements and considering its long-term performance and energy costs. The more pragmatic solution is to use high efficiency products that are already future proofed for legislation and ErP compliant. After all, the payback for clients will be far quicker, and the on-going energy efficiencies will make it a sound investment.