Go with the flow - July 2013
This article appeared in Heating, Ventilating & Plumbing, July 2013
MVHR units are subjected to strict testing at the end of the production line to ensure a consistently high standard of product performance is achieved. Yet despite the quality of the products, the performance of the installed system is still dependent on the standard of the installation. Paul Rainbird, Operations Manager at Titon, reviews the current test methods and highlights the key points to ensure successful commissioning.
Looking back over the last couple of decades, the housing sector has gone through some monumental changes, with a quantum leap in the design philosophy of residential buildings and components. Of course, throughout this evolution, the development of the core range of products used in new houses has led to considerable gains: boilers have become more efficient, windows have reduced U-values and loft insulation is, quite simply, thicker. As a result, one product that has been thrust to the forefront of the industry’s developmental race – and looks to become firmly embedded in its ethos – is mechanical ventilation with heat recovery (MVHR).
Unsurprisingly, this transition has been born out of the energy saving demands, to conserve the planet’s resources and our bank balances when it comes to paying our fuel bills! Numerous factors have played their part, including changes to Part L and Part F of the Building Regulations, the Code for Sustainable Homes, and greater awareness of the of need to maintain good indoor air quality in the wake of increased airtightness. Yet despite all the benefits associated with the MVHR movement, ventilation systems are still dependent on the quality of the installation and the commissioning process.
It is all well and good to carry out testing of the MVHR unit only on a rig in laboratory conditions, but it’s an altogether different scenario onsite with a whole system, ducting, terminals and units. This has led to documents such as the Approved Document F (ADF) of the Building Regulations and the Domestic Ventilation Compliance Guide 2010 (DVCG) which accompanies it, being developed to help reduce the risk of potential problems.
When it comes to comprehensive commissioning of MVHR systems, it’s vitally important to ensure the unit and systems are operating effectively and efficiently and a key element of the process is to check that the system has been installed ‘as designed’. This is particularly significant for MVHR systems, as installed variations to the intended design can lead to major problems such as unacceptable energy inefficiencies or negative impacts on airflow performance.
The main task of the commissioner is to set and balance the fan speeds in the main unit, and adjust valve apertures in each of the rooms to ensure the minimum of energy is used in achieving the necessary airflows. This requires the use of a calibrated air flow device and the DVCG recommends that a vane anemometer is used to balance and measure the air flow rates at each room terminal and at each of the fan setting, normal and boost. Plus, ideally, flow rates on both the intake/exhaust side, as well as the extract/supply side, should be balanced. It’s at this point that many problems are often identified as rates cannot be achieved at the anticipated fan speeds and often too late to avoid expensive remedial works as many components are no longer easily accessible.
Another critical part of the commissioning process is ensuring user controls are identified and understood by future occupants so they can easily use the system. MVHR units will vary depending on a particular manufacturer’s product range, and understanding the various bypasses, boosts and seasonal settings in a system is imperative in allowing effective use. Ensuring the user knows how and when to operate the controls is extremely important to guarantee the ventilation system operates at optimum efficiency all year round.
Finally, it is recommended that MVHR systems which are intended to run continuously are also designed to minimise the risk of noise disturbance. After all, a noisy system is likely to provoke user interference, which could result in reducing the effectiveness of the system or turning off the unit altogether; either of which would undoubtedly inhibit efficiency, as well as threaten the health of the occupant and the building fabric.
So, with MVHR becoming more prevalent in new builds, and accurate design installation and commissioning is key to the technology’s success, what of the future? Well, the Building Regulations, DVCG and the accompanying Part F have certainly given whole house ventilation greater prominence in the industry. This, in turn, has helped improve the quality of installations and the commissioning process. It’s imperative that the standards outlined by the legislation and the manufacturer’s guidelines are strictly adhered to, otherwise, the long term energy savings offered by MVHR technology could be undermined.
Overall, there seems to be a consensus in the industry about the wisdom of harnessing the heat normally lost through necessary ventilation as other means of reducing heat loads, such as airtightness and insulation, are maximised. The technology is now advanced and undoubtedly an important part of cutting edge new build design and MVHR will soon become a ‘must-have’ system in all new build homes.