By 2016 all new build homes must be zero carbon, and already several standards promote airtight homes. But Derek Guy of Itho Ventilation explains that it is important to understand the repercussions of this energy efficiency method before efforts to seal up dwellings are undertaken.

The raised standards of Part L of the Building Regulations, the Code for Sustainable Homes and the guidelines set by the Energy Saving Trust all promote the benefits of airtight homes in the quest to reduce energy wastage.

With the necessity to meet level 4 of the Code in the public sector looming in April 2010, it is envisaged that specifiers and property developers working across both the public and private sectors will apply the public sector standards in their private sector projects at the same time, thus setting the trend for the industry to follow.

While building an airtight home dramatically reduces heat loss from a property thus helping energy consumption levels to remain low, without a continuous flow of fresh air into the property the internal atmosphere will become stale and full of contaminants which, if not removed, will cause countless problems with condensation, mould growth and aggravated health problems for the occupants.

Traditional forms of ventilation will not meet our future needs. Standard extractor fans cannot offer the energy efficiency performance required for the latter stages of the route map, while opening windows causes expensively generated heat to escape and lets pollution and, often, unacceptable noise in. This means there will be an increased use of continuous ventilation.

While the words ‘continuous running’ and ‘energy saving’ are rarely used in the same sentence, continuously running fans can now be more efficient than intermittent fans. Two whole-house ventilation systems available on the market are MEV (Mechanical Extract Ventilation) units, and MVHR (Mechanical Ventilation with Heat Recovery) units. Both allow a continuous flow of fresh air to circulate throughout the dwelling, drawing and expelling the contaminated, wet air from the areas that need it the most: the kitchen/utility, washrooms and bathrooms.

The running costs of such a system are very low and help reduce fuel bills. Take for example a two storey building with a habitable floor area of 88.2m2 and kitchen plus three additional wet rooms (utility, bathroom and WC). To meet current building regulations the system needs to extract at a continuous rate of 26.5l/s and be able to boost up to a minimum of 35l/s. Excluding air infiltration rates from the calculation, the air tightness of the building is 1.5m3HR/m2.

Based on a BRE survey, this indicates that the intermittent fans were used for two hours per day. If one of the Itho HRU ECO 4 units were to be installed and commissioned correctly, the unit would consume 14W on low speed (1), 39W on medium speed (2) and 86W on high speed (3). Looking at the energy usage of 1, running continuously for 22 hours per day and speed 3, on boost for two hours per day, this works out to 175.2kw per year. Based on USwitch.com rates in July, the cost would be £16.42 per year. The savings made on the reduced heating needs of the dwelling will more than offset this cost.

Continuous MVHR is proving to be the modern solution. A continuous balanced system can be positioned in a loft or cupboard space. An integral heat exchanger recovers a large percentage of heat energy that would have otherwise been lost. In employing this type of system, there is no need to install background ventilators in the dwelling.

As featured in the Energy Saving Trust’s Demonstrating Compliance: Best Practice, in order to meet reduced CO2 emission targets, MEV and MVHR units have been set certain standards. MEV units must have a specific fan power (SFP) of 0.6W/l/s or less and MVHR units must have a SFP of 1.0W/l/s or less and a heat exchange efficiency of 85% or above.

One efficient and versatile MEV unit is the Appendix Q eligible CVE ECO 2 which is equipped with a quiet, low consumption DC (direct current) motor that ensures the unit functions using considerably less energy than conventional MEV models.

Allowing for an even greater level of efficiency to be reached, the Appendix Q eligible MVHR unit– the HRU ECO 4 - offers heat recovery efficiency and specific fan power of <0.5 compared to SAP currently at 2.0 and Energy Savings Trust at 1.0. Even though it achieves heat exchange efficiencies up to 91% it is this SFP where the real money is saved.

By introducing a heat exchanger, where both the incoming air and outgoing air pass through the system, heat is transferred from the extracted contaminated air directly into the incoming fresh air and with this technique a dwelling can maintain a large percentage of its optimum temperature as less heat is wasted through the extraction process.

This system enables designers to structure an effective ventilation solution to any home when planned as part of the building design at an early stage. However, a poorly designed and incorrectly installed ventilation system can negate all that it is designed to do. For example, it can dramatically reduce ventilation and, in some cases, render it non-existent, due to poor planning and installation. It can also fail to meet the minimum ventilation requirements in approved document F of the Building Regulations, and can necessitate expensive reworking to the ducting.

http://www.itho.co.uk