Can I avoid using a Mechanical Heat Recovery Ventilation System?
Yes, but it makes no sense to do this. Let us explain. If you ventilate the house ‘naturally’, then you can only recover at best a relatively low proportion of the heat being lost from expelled air (40% heat recovery when ventilating naturally, compared with 85%+ with mechanical ventilation with heat recovery). Using what is referred to as a passive stack ventilation system will operate best when there is a substantial difference between indoor and outdoor temperature – this condition might not occur at certain times of the year, especially in the summer and thus you cannot be certain of achieving sufficient air exchange rates at all times in all rooms. Remember too that the ducting system used in the ventilation is used not only to transport fresh air around the house, but also to convey the back-up heating required. If you do not put in a mechanical ventilation system, you will probably have to install a conventional heating system (such as under-floor heating or radiators) incurring cost which might have paid for the ducting in the first place. Lastly, it has been well proven that ventilation systems are extremely efficient, provide a controlled ventilation rate throughout the house and ensure clean air through the use of filters.(PHPP Software) by experienced Passive House experts.
Is it unhealthy to live in an ‘air-tight’ house?
No, because the house is provided with lots of fresh air using a ventilation system. One of the main benefits of building a Passive House is the high air quality. In normal houses, fresh air enters the building though a series of ‘hole-in-the-wall’ vents and / or through drafts. However, such means of ventilating are uncontrolled and you cannot be sure that all rooms at all times are being properly or sufficiently ventilated. The entire volume of air in a Passive House is changed on average between 8 to 12 times per day (depending on the setting of the system) ensuring very high air quality throughout.
Doesn’t the ventilation system use a lot of energy?
Surprisingly, No. The air is delivered and extracted using two fans which use very little electrical power. As a rule of thumb, for an average house, the system would use a similar amount of energy as a 50 Watt bulb costing approximately €75 per year. Please note, that a highly efficient Passive House ventilation system should recover approximately five units of heating energy for every unit of electrical energy invested. Thus, the system might cost you €75 to operate per year, but could save you €375 per year in heating bills. If you are not happy using electrical energy to operate such a system, then you can use some means of generating your own power on-site such as with a wind turbine or using photo-voltaic panels. This will, however, significantly increase the cost of your project.
What is it like to live in a Passive House?
Great, Fantastic. A Passive House will provide a long-life, low maintenance, light-filled and whole-house high comfort with extraordinary low heating bills and excellent indoor air quality. Plus, you can feel very proud of yourself for dramatically reducing your carbon footprint. ‘Inwardly satisfied’ probably best sums it up!
Is the ventilation system noisy?
No. The ventilation system itself is housed in a very well insulated and airtight cabinet which is normally positioned in a utility room. The noise from the fans is no greater than that from a modern fridge. The ducting is fitted with what are referred to as ‘attenuators’ which reduce the sound of air passing through the system. In bedrooms the system, if properly fitted, will barely be audible at normal flow rates.
Can I be sure that my Passive House will ‘work’?
Yes, of course. It is essential, however, that the house has been properly designed in PHPP and then well-executed on-site achieving the required levels of airtightness and low thermal bridging. There are over 15,000 Passive House’s throughout Europe, providing very high levels of comfort in climates that are much colder than that of Ireland.
What happens if there is a power-cut?
Similar to normal houses, all mechanical systems will cease to work. However, because Passive House’s are so well insulated, they will maintain a higher level of comfort for much longer than would a normal house in the event of a power failure. If the power cut lasts for a prolonged period (say, more than 12 hours), then the windows can be opened to provide fresh air if required. Power has been cut off to MosArt’s demonstration Passive House several times over the past few years (due to grid works in the neighbourhood) and this has never caused any inconvenience or discomfort. Carbon monoxide alarms can be fitted in the house to detect reduced air quality.
Can I connect the kitchen extractor to the ventilation system?
Yes, but it is more prudent not to do so. The benefit of connecting the extractor in the kitchen to the ventilation system is that you can use the heat generated in the process of cooking to warm the incoming fresh air. However, if you choose to do this, then there must be special filters on the end of the ducting eliminating any fat or grease getting into the ducts which would create both a health hazard and a fire risk. Furthermore, it must be possible to access the ducting located immediately above the extractor hood for occasional cleaning and / or replacement. It is safer to use a re-circulating extractor (not connected to the outside) with a charcoal filter, with the ventilation system extract located in the kitchen space but not close to the hob. Note: kitchen extractor hoods in a centralised ventilation system (as might arise in an apartment complex, for example) should never be connected to the mechanical heat recovery ventilation ducting due to risk of fire spread.