Where do you start when it comes to ventilation?
1. Choosing the right ventilation strategy
2. Choosing the right type of ventilation system
3. Specification of the air flow rates in each room
4. Choosing the best type of ducting
5. Choosing room and external terminals
2-5 is included in our free specification & cost proposal
6. Detailed ventilation design
7. First fix of ducting
8. Second fix of the system
9. Commissioning & handover
For new build homes, the designer and customer need to decide if the house will be ventilated naturally or mechanically. This choice mainly depends on the target air tightness of the property. Only relatively leaky buildings suit themselves for natural ventilation with intermittant extract fans. All other dwellings need a continuous ventilation system.
For continous systems, Building Regulations specify certain ventilation rates, mostly based on the internal floor area and the number of habitable rooms (Scotland) or bedrooms (England & Wales).
For existing dwellings, that are being upgraded to a certain degree, there needs to be an assessment of the existing ventilation provision done and possibly a revised ventilation strategy.
If Heat Recovery Ventilation (MVHR) is chosen, it is recommended to build relatively air tight (less than 5 m3/h m3 @50Pa), better less than 3 m3/h m3 @50Pa, to capture as much energy savings as possible.
More leakier homes will still benefit from the MVHR, its de-humidifcation effect and its filtration of the incoming air. Even at air tightnesses of up to 8 m3/h m2 @50Pa, MVHR have shown to still save energy, compared to Natural Ventilation.
In some cases, when dwellings are situated close to busy roads or flight paths and occupants are not expected to open their bedroom windows at night, MVHR will need to be specified.
For continuous extract ventilation the choise is between:
If a balanced system (MVHR) is specified, there are following choices:
Each of these systems have their specific advantages and disadvantages.
Almost unnoticeable when comparing data sheets, there is a massive difference, between standard UK MVHR systems and those with Passive House certification. Please compare the level of insulation on the housing, the type of frost protection, controls and filtration. See here for more details.
In most cases we would recommend Passive House certified MVHR systems for any type of house.
Often cost is the most predominant consideration. However, the health and wellbeing of the occupants should not be overlooked. Good MVHR systems with pollen filters can make a huge difference for the occupants. See here for a case study
Building Regulations set proposed calculation methodologies for the air flow rates. Unfortunately these are not designed to air quality targets in specific rooms, which often leads to poor IAQ in bedrooms. When spending money on a MVHR system, would it not make sense to specify to good indoor air quality instead? That is why we specify like no other company in the UK.
We also optimise the air flow according to the design specifics of each dwelling, through e.g. the incorporation of the cascade effect, taking the usages of various rooms and their heat input into account.
The right ducting is important for the performance and longetivitiy of the ventilation system. Think about: How often will you expect the ducting to be changed in the next 50 years? Probably never. A good ducting system needs to be:
We offer following types of ducting, as part of our no-compormise policy:
For very small ducting systems in flats, the branch ducting is more efficient, as well as for long-streched buildings with high air flows. For most other dwellings the radial system is the cheaper and better solution, without compromise on performance.
We always recommend powerful noise attenuators (silencers) for the supply ducting, and normally also for the extract ducting, in order to make the system inaudible within the dwelling. Good noise attenuators are 500-1000mm long (see rectangular metal box in the picture).
We offer high-quality designer room terminals as standard: Lindab Airy. These powder coated metal terminals integrate nicely into ceilings and walls with their flush appearance. They can be used for supply and extract air and avoid drafts and are the quietest on the market.
For wall supply terminals, we recommend in most cases a wall diffuser or jet valves.
We normally specify a filtered extract for kitchens, which prevents grease being drawn into the ductwork. The visiable filter material promts a regular cleaning or exchange, whereas a hidden filter cone can easily be forgotten and block the extract.
When regular cooking is intended, a re-circulating cooker hood with active charcoal filter can be installed, which filters our grease and smells.
For use with high-flavour cooking, increased ventilation rates are recommended.
A good ducting design is vital for a successful installation. We offer a design to true best practice standards, based on 3d design tool Revit for all bespoke designs. Our dedicated, Scotland-based design team is taking our customers’ needs into consideration. In our chargeable design service are up to 5 iterations included free of charge.
When it comes to the installation of ductwork, plenums for room terminals, attenuators and manifolds, we find that self-installers can do a good job, when they are given a detailed design drawing and have some project support. That’s why we have a dedicated Project Manager to answer all questions and assist as needed.
For professionals, we offer in-house installer training (BPEC course on Domestic Ventilation).
The second fix entails the installation of the MVHR unit, the room terminals and the connection to the external terminals.Following trades need to prepare for the second fix:
Every system need some form of commissioning, which means inspection, testing and adjustment. Then a commissioning report needs to be produced for Building Control. Also, it is important that any ventilation system is handed over to the end-user with a simple user guide. This increases user acceptance and the correct use of systems.
We offer an accredited commissioning service in central Scotland and Norther England.
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.
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)
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).
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).
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).
The recommendation is a staggered approach, depending on the air tightness of the building envelope:
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).
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:
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 inOpen the file with MS Excel.
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 calculationsPlease 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
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In an industry with very little training and experience and a widespread lack of attention to detail, we would like to offer an all-round service around domestic MVHR systems, in order to make every project a successful one.
Find our more about MVHR systems, their advantages and disadvantages and how they can be implemented.
Information on domestic ventilation strategies, ventilation rates, Passive House ventilation and specification.
Information on how to install & commission MVHR systems in dwellings.
We support developers and building companies for housing developments, whether to Passive House standard or not.
Get inspired by some exciting projects and listen to our customer’s experience.
If you want to commission us to carry out an MVHR design, please find this checklist as a help to provide all the information.
If you want us to carry out an installation of a MVHR system, this checklist will help you determine when the building is ready for the first fix.
If install of a MVHR system for you, this checklist will help you determine when the building is ready for the second fix.
If you want us to commission a MVHR system, this checklist will help you to determine what needs to be done beforehand.
01383 221 255
info@paulheatrecovery.co.uk
© 2024
Sustainable Homes Scotland Ltd
t/a PAUL Heat Recovery
Unit D, Pitreavie Business Park
Pitreavie Crescent, Dunfermline
KY11 8PU Scotland
Registered in Scotland – CRN: SC331209
Directors: Stefan Huber, Allan McEwan, Garrie Glasgow
