We Keep You Right

Building a new home or a cluster of new dwellings? Do you want to make a quality home?

Historically dwellings were valued according to their size, their layout, their location and their standard of kitchen and bathroom finishes. Nowadays the value system is shifting towards recognizing the energy efficiency, renewable technologies, sustainable materials and other aspects of sustainability – and rightly so.

For new build homes we can simplify four energy efficiency standards.

Leaky Standard energy efficient dwelling

This is now the exception in new builds, which are just fulfilling the current demands of Building Standards.

Building Fabric: Standard insulated, double glazing.

Air tightness: 5-10 m³/(hr m²) @50Pa.

Heating & DHW: typically either a gas combi-boiler with radiators or a heat pump with underfloor heating.

Ventilation: Natural ventilation with intermittent extract fans, trickle vents in all windows or dMEV Systems (no trickle vents)

Standard energy efficient dwelling

This is the typical mass house builder home. Their energy standard is just fulfilling the current demands of Building Standards.

Building Fabric: Standard insulated, double glazing.

Air tightness: 3-5 m³/(hr m²) @50Pa.

Heating & DHW: typically either a gas combi-boiler with radiators or a heat pump with underfloor heating.

Ventilation: often dMEV fans (trickle vents in habitable rooms only), better: MVHR Systems (no trickle vents).

Low energy dwelling

These are homes that often they incorporate the ‘Fabric First’ approach, with better insulation and air tightness.

Building Fabric: Good insulation level with double or triple glazing.

Air tightness: 1-3 m³/(hr m²) @50Pa

Heating & DHW: various technologies are being used. We can help with far-infrared heating panels and solar assisted heat pumps for hot water.

Ventilation: MVHR (no trickle vents) or cMEV systems (trickle vents in habitable rooms).

Passive House dwelling

These homes have excellent energy efficiency levels, often in conjunction with renewable technologies.

Building Fabric: Excellent all-round insulation level with triple glazing.

Air tightness: 0-0.8 m³/(hr m²) @50Pa. For certification an air tightness of 0.6 ach@50Pa need to be achieved. A dedicated internal air tightness layer is being used.

Heating & DHW: various technologies are being used. Please note that Passive House dwellings still need a heating system. In many cases this is a downsized central heating system. In the beginning of Passivhaus their space heating was achieved with post heaters in the MVHR. In many ways this concept has proven challenging. We have successfully implemented it in many ways, but for larger dwellings we would recommend to separate the ventilation from the heating system. We can help with far-infrared heating panels and solar assisted heat pumps for hot water.

Ventilation: MVHR systems to Passive House standards (no trickle vents).

What does Building Control in Scotland recommend for new domestic buildings?

The recommendation is a staggered approach, depending on the air tightness of the building envelope:

• If the building is very airtight (0-3 m3/(h m2) @50Pa), the only choice is Heat Recovery Ventilation (MVHR)
• If is it semi-airtight (3-5 m3/(h m2) @50Pa), either MVHR or dMEV can be used
• If it is lesser airtight (5-7 m3/(h m2) @50Pa), either dMEV or natural ventilation can be used. MVHR is possible, too, as there are different reasons for the use of this technology, other than the air tightness of the building.

A problem arises when the measured air tightness of the building is very different from the target air tightness. In such cases often the ventilation strategy needs to be revised. What complicates the matter is that the air tightness test needs to be carried out when the building is finished. At this point remedial measures are very difficult to implement. E.g. the architect specified 5 m3/(h m2) @50Pa with natural ventilation and trickle vents. Now the trades have done a good job and the building achieved 2.5 m3/(h m2) @50Pa. This means MVHR needs to be retrofitted into the finished building.

Looking at the reality of the building industry, it is often difficult to predict the real air tightness of the building, as much depends on the workmanship of the trades. It is probably the better approach to plan for a solution that complies with the tighter standards, e.g. MVHR.

We find the best choice of ventilation strategy is MVHR – if it designed, specified, installed and maintained right. There are some cost implications, but the comfort and air quality will pay dividends (over and above the energy savings).

Alternative ventilation strategies:

dMEV is a much cheaper solution in the initial expenditure, but as these don’t recover any heat, with the expelled air all the heat energy is lost. Such fans are better versions of extractor fans, that run constantly on a low level and boost when necessary, e.g. when they detect increased humidity. Modern dMEV fans are very quiet.

 recent research in Scotland has shown, that most dMEV systems do not deliver the desired indoor air quality? The reason is, that the ventilation path through the building is much less controllable than with MVHR systems. E.g. some bedrooms might have very little to nearly no ventilation at all. dMEV systems need to be carefully specified to avoid such downfalls of the system.

Natural ventilation via background (trickle) ventilators with mechanical intermittent extract fans is still an allowed ventilation strategy for ‘leakier’ houses, but…

 that in practice hardly any new built house will achieve the legal requirements for indoor air quality, unless occupants open window regularly? As such natural ventilation alone is not fulfilling the demands of Building Standards and therefor it is not a viable ventilation strategy. Occupants need to co-operate, e.g. keeping windows of bedrooms in use tilted all night (without curtains or blinds blocking the ventilation path) and cross-ventilate during the day every couple of hours.

Demand operated cascade heat recovery ventilation is the ideal partner for holiday accommodation. Such dwellings often suffer from increased levels of humidity, because the moist air at the end of each occupancy cycle can’t escape as the building is locked. The humidity subsequently condenses on the walls and surfaces, as the building cools down and over time this can cause mould and fungus infestation.

This danger will be avoided through constant ventilation and active de-humidification of an MVHR system. With the help of demand controlled operation, there is no necessity for any user interference. The system will adjust automatically to the changing occupancies and usage cycles.

However all air quality values, temperatures and the energy consumption can be remotely monitored through the integrated smart software link.

We recommend fully autmated systems, e.g. the bluMartin freeAir 100 or the Zehnder ComfoAir 70 MVHR system for smaller holiday dwellings as it is fully demand controlled and as such will adjust to the changing use automatically.

If you want to calculate the ventilation requirements according to current Building Standards, please follow the following three steps:

1. Download

If you have MS Excel on your computer, please click on the link on the right hand side (Calculator for England Wales) to download the Excel file.

2. Fill in

Open the file with MS Excel.

1. Fill in your site address and post code into the spaces in row 2. If you don’t have the post code, please leave it blank.
2. Choose from the Building standard (Scotland, England, Wales or Northern Ireland) and choose your ventilation rate output (m3/h or l/s).
3. Now you can fill in all the rooms of your dwelling from row 19 onward. Each room is normally a separate row. Choose the room type (as per drop down) and then fill in the room name if it deviates from the type, e.g. Bedroom 1, Sitting Room, etc.
4. Calculate the floor area in square meters, e.g. if the room is 4.5m by 6m then fill in =4.5*6 in column G or just type the floor area e.g. 27. If you only have dimensions in square feet, then multiply the result by 10.75 to convert Sqft into m2.
5. You can add the room heights. In Scotland this is capped off at 3m.

3. Save and send

Save your excel file and send it to us with your floor plans and section drawings (if you have these).

Please send these to enquiries@paulheatrecovery.co.uk

We will aim to come back to you with a specification and cost proposal within one working day.

Some comments on these calculations

Please note that the calculations are preliminary only. The Building Regulations are a safety net to avoid major disasters. To just apply these without consideration of the real needs of the dwelling as whole and each room in particular is in many ways not reflecting best practice standards. Every ventilation design needs to be looked at individually and adjusted to the varying needs of each dwelling.

Following room types need to be looked at in more detail:

– Master bedrooms and bedrooms that are regularly occupied: These should have a minimum ventilation rate of 20 m³/h ventilation per person (at trickle = nominal level).

– Walk-in wardrobes: If these are connected to the bedroom without doors then they can be treated as part of the bedroom and do not need a separate air terminal. They will be ventilated by convection.

If they have a door and have a floor area of more than 4 m², we would recommend to install a supply terminal with a low flow rate. Smaller wardrobes normally have no air terminal.

– Store rooms and cupboards: If these have a floor area of 4 m² or more, it is recommended to install an air terminal. This can either be a supply or extract terminal, as these rooms are neither habitable rooms, nor wet rooms or rooms with pollution. We would recommend to install a reduced extract rate. Please note that our proposed flow values are not part of the ADF recommendations.

– Open plan living/ dining rooms and kitchen: It is advisable to treat a dining room, which is sandwiched between a living room and a kitchen as a through room, unless there is a specific reason to install an air supply terminal there.

– Hallways, stairs and landings are typical through rooms without air terminal.

There is much more to consider, but these are just the basics.

PS: Please note that we do recommend the Passive House Guidelines as a far more demand oriented specification tool than basing the ventilation rate only on 0.5 ach, independent on the room type.

“I cannot recommend PAUL Heat Recovery Scotland highly enough. They know their products, offered us intelligent & helpful advice on MVHR before we bought our system, and have always been prompt & friendly in their replies to us.
Since buying the system, their customer service and aftercare has been exceptional in every way. Stefan & the team have answered all our queries, given us help & advice, and sorted out various teething problems for us at a distance and at no cost (and all the problems were caused by the installers, not the system itself).
I have rarely had such great service and support from a retailer, and I’d wholeheartedly recommend them to anyone.”  Adam from East Sussex