Self Build air tightness test -0.22ach with a volume of 603 m3 @ 50 pascals.
When one is building to a performance standard the day of reckoning is the airtight test. The reason for this is that when one is pumping fresh air into the house using a Heat Recovery System, rather than relying on simple multiple holes in the wall, it becomes important to control where the fresh air is coming from and where the heat is going.
If air is leaking in or out around windows /doors/walls or other gaps in the building fabric then heat is lost and moisture problems in the form of mould can arise or else give rise to damage to the building fabric.
The pressure 50 pascals equates to a 20 mile per hour wind which is not too untypical in Ireland. So if one opts for the Irish building standard (a minimum standard) this equates to the air in the house changing/leaking 7 times a hour when a wind blows at 20 miles per hour. No wonder people block up the hole in the wall vents .
The current Irish building standard require 7 air changes per hour (ach) also called leakage at 50 pascals typically with no heat recovery system. As a guidance heat recovery manufactures recommend 3 Air leakages per hour to ensure that the heat recovery system can push fresh air into the house and recover heat leaving the house through its own system rather than through gaps in the building fabric.
The passive house standard for a new house requires 0.6 Air changes per hour (ach) at 50 pascals to ensure the heat recovery system works efficiently, ensure that occupants receive the correct amount of fresh air and minimise building fabric damage.
The passive house test differs from the Irish test because it must include pressurisation and depressurisation and use the volume as set out per Vn50 (EN13829).
Gavin O Shea from Greenbuild was hired for the job. He is certified/audited by the National Standards Authority of Ireland (NSAI).
The preparation for this entailed sealing all cable ducts and the inlet and outlet pipes for the Heat Recovery System. One also ensures that the shower and sink outlet traps are full of water. The overflow outlet for two water tanks were not sealed off. I did consider a duck valve but it was not in place at the time of the test.
The test using the Irish method gave a result of 0.181 m3
Gavin O Shea calculated that the equivalent size hole that equates to a result of 0.22 ach is approximately 65.25 cm2 (@50Pa) or a hole 81mm x 81mm if all of the leaks present in the dwelling were concentrated into one hole. That is about a tenth of an A4 sheet of paper.
The results of the air tight test can also help determine the selection of the Heat Recovery System. If the airtight test is lower then more options are available when selecting a unit.
From my research a passive house standard Heat Recovery Unit will cost more because it needs to be independently tested by the Passive House Institute using their test method. Heat Recovery manufactures have also the burden of putting the unit through national tests or international tests with the end result being the customer pays more. One has also the option to select a non passive house certified unit for a passive house but when calculating the performance value one needs to account for this in the PHPP software with a 12% reduction below the manufacturers performance claim.
If one wants to view certified Heat Recovery Units one can find and sort them at the following link. One can see for example at this link the capacity (Column- Air Flow Range) that these units have as it is important to select a unit that is oversized for your particular self build. I would compare it to selecting a mini car to tow a caravan up a hill compared to using a larger car. The small car will struggle from an efficiency and noise point of view while the larger car will be quieter and more efficient at the require flow rates. I will do a separate post on how I selected our Heat Recovery Unit.
I came across information over the years that may help the self builder when it comes to retrofits (doing up an existing dwelling).
This is probably the most challenging of self builds as the options are few when it comes to insulating a house that was never designed to be insulated.
The other problem for the self builder is how well were the houses built in the first place -are the construction details good?. If they are good then it may be an easy step (it is evident that today there are problems with new builds. Could it have been any different in the past?)-for example were the cavities clean, state of repair of pointing, brickwork etc., .
A Guide to doing it right
The document below is a very good guideline on renovating an old building correctly when it has solid walls.
Check for any newer versions at their web site.
I extracted a sample of the contents from the above guide by way of example.
It also needs to be realised that by adding insulation to a wall that was not designed for insulation can make the house colder if the solution is not correct, structurally damage the wall over time or cause mould on the inside that may affect your health. The above report goes through this.
The above will hopefully guide the self builder away from the problems and find the correct solution.
One needs to fully understand that one needs to choose the most robust solution that can withstand something going wrong.
Some of these products may be safer to use when it comes to old buildings . Some require extra measures to ensure they keep the building dry and you warm.
The hot water tank is a 300 litre stainless steel tank. Stainless steel is better at reducing stratification (minimising mixing) because it conducts less heat compared to copper. Different grades of stainless steel exist for different types of water (hard/soft). One also needs to check the type of welds used on the tank as some can not cope with certain water types.
The tank was modified to allow me to connect the solar PV water heating system (previous blog) in the future using thermosyphonic action i.e. hot water is lighter than cold water so it naturally flows from the top of the tank to the bottom (Reducing the need for pumps). The DC power from the solar panels will be connected to electric heating elements. As the solar power varies the heating elements will adjust the output power through a control unit I am developing.
IfI install a solar hot water system or another method in the future this will be done with a plate heat exchanger rather than a coil. I installed extra connections on the tank for this reason. The reason for the heat exchanger is that the tank will heat from the top down. A plate heat exchanger looks like the following
If one opts for a coil it creates turbulence while heating the tank. I found it difficult to find a tank manufacturer who will install the correct surface area of a coil for a climate like Ireland. I feel most are designed for hot countries like Spain where the sun shines and stays shining. If one opts for a coil rather than a plate heat exchanger one requires a large coil surface area to ensure that most of the solar energy transferred in the least amount of time and the temperature returned to the hot water solar panel is at a minimum. In this way the hot water solar panel can operate at its maximum efficiency.
Initially when researching the options available to plumb the house I came across two main methods- Pressurised/Closed or Gravity/Open. I settled for a gravity based system because of the simplicity, DIY, reduced parts and maintainability. If one can increase the height of the gravity tank the pressure will increase at the taps.
Below is a video of what a pressurised/closed system can do (if it goes wrong and probably very rarely). When I was researching pressurised systems I felt that there seemed to be different ways of designing these and providing the necessary safety levels. I do not like systems where there are potentially hidden failures (when a safety device is supposed to work and does not).
I also was hoping to use gravity to supply the showers but it is becoming more difficult to find a good choice of shower valves and shower heads that work on low pressure . The way around this to keep things simple is to install a shower pump in a central location for two of the showers (see below). One can then use a shower head that helps control the flow rate and keep the water use to a minimum.
For one of the showers I already have a shower valve and head that works well on gravity so I will plumb this separately directly from the tank (shower 3 in the layout below).
The plumbing layout for the house is shown below. (The toilets are fed from a separate gravity tank supplied by the rainwater harvesting system as shown on a previous blog.)
I am using Qual-Pex for the plumbing in the house. It varies in price so it is a good idea to shop around (The 1/2 inch varies from €70 to €200 for the same pipe). I ended up using 200 metres of 1/2 inch and nearly 50 metres of 3/4 inch and 25 meters of the 1 inch.
The overflow from the tank needs to be well secured or finished in copper to ensure that if the tank overheats the pipe will not sag/bend or cause a restriction.
The brass fittings are cheaper than the quick connect so I will use these. One needs a good plastic pipe cutter as using a hacksaw is not feasible. I used a Ridgid brand plastic pipe cutter and I am very happy with the quality.
With a plumbing design one needs to ensure that the size of pipes are no bigger than they need to be. One reason for this is that the volume of water in the pipe will cool down and one has to wait for this to run through fully before getting hot water at the correct temperature.
I calculated that 10 meters of 1/2 inch pipe holds approximately 1 litre of water and 10 meters of 3/4 inch holds 2.3 litres. This gives one an idea if a solution is required and the wait time.
The cold water pipes will be insulated as I am concerned that condensation could occur on the surface of the pipe.
I also tried to ensure that the number of connections/joints are kept to a minimum and I tried to place these only at accessible points.
Logistics of getting hot Water to the furthest points.
The kitchen sink hot water supply is too far from the tank so I may develop an on demand system that ensures hot water is available once certain taps are used rather flushing semi warm water down the drain and a one or two minute wait for hot water. Installing instantaneous heaters is not economical.
A way to solve this is only use one 12 volt pump and have a valve at each sink position. This pump will then feed into the gravity header tank rather than the hot water tank (I need to check the regulations) . I want to keep the plumbing connections and electrical devices to a minimum. The power to operate this can be a small solar panel charging a battery.
The plan is to develop a solution around the following -Measure the hot pipe feed temperature, Detect if the tap is going to be used and link this to controlling the pump and valve.
The only item that needs to be purchased is a 12 volt pump and a 12 volt valve and develop the control unit to suit the Irish regulations. I have started on the design of this. In the meantime I will install a third pipe in the bathroom and kitchen for the final solution.
It is now time to research the solutions available in order to guarantee a fresh air supply into the house, extraction of the stale air and recover heat before the stale air is sent on its way.
There are a number of options -Use the hole in the wall in each room (with no heat recovery), use a central extract system (with no heat recovery), use decentralised heat recovery or a fully ducted heat recovery system .
From previous experience and research the hole in the wall system does not work well taking into account that we have a wind speed of almost twice that of Germany. The system creates draughts and one has only to view the number of vents blocked up and the dependence on the correct speed of wind blowing to supply fresh air in Irish dwellings to realise it does not work.
The central extraction systems either using the stack effect (using temperature differences between the inside and outside) and Bernoulli’s principle (using wind) with no fans is an option. One can use extraction systems that are powered by fans. These do work it appears but they need careful design .
Localised vents in different rooms that use heat recovery such as the Lunos , Aereco and Glidevale iMEV system offer powered heat recovery but when I priced these they were more or less the same price as a fully ducted system and require more holes than I want through the fabric of the building.
Another system recently certified by the Passive House Institute is a heat recovery system that requires two units at either end of a building called (fresh-r). I can see the system working in an open plan environment but the cost is more or less the same as the other solutions above.
If one wants to compare certified heat recovery systems one can use the certified component list on the passive house web site Certified Heat Recovery Products. These products are independently tested by the Passive House Institute.
I will be selecting a centralised heat recovery system because I feel if it is specified, designed , installed and commissioned correctly it offers the best solution. I also plan to use it as a clothes dryer in order to get extra value out of it.
What is in a typical centralised Heat Recovery System,
It typically has two energy efficient fans, a plastic heat exchanger, filters to clean the air, enclosed in an airtight box and a means to control the fan speed. It is a simple unit but the cost is high (in line with the price of other systems above except for the hole in the wall or a stack system)
I was informed recently that the Passive House Institute charges heat recovery manufactures around €60,000 for testing and certification and then there are ongoing yearly costs that need to be passed down to the consumer. A Heat Recovery Company also needs to pay for National test (separate to the Passive House Institute) in different countries which also needs to be passed down to the consumer. There appears to be no European standard test that can satisfy all EU countries.
The product I was originally interested in was from a company called Paul but for some reason the price has risen substantially- I received a price for a Paul 450 unit two years ago and it was €2000 . It is now nearly €3000 -why?. One reason is that that the product was taken over by another HRV supplier Zehnder. I will try not select these products as I see no reason why the price of the unit increased by nearly a €1000. The price above is for large air supply volumes. A three bedroom house may only need a small unit costing 50% less.
One of the highest energy efficient certified units available is from a company called Maico-an Irish representative is available. Prices start at around €2400 for a more efficient unit than the PAUL unit . Other options are from Brink such as the Excellent 400 plus also available in Ireland. Systemair Gmbh also have units available in Ireland.
I did not think this area was going to be as complex as it is. Lets start-there are different choices of ducts from metal round, plastic round, flexible round, rectangular and all other types of shapes. The bottom line is that large round metal ducts (150-200mm) are the most efficient and quietest and have the lowest air speed.
The flexible ducts vary between two types either Aluminum or Polyethlene with general sizes between 125mm (steel), 90mm, 75mm and 65mm. The smaller the duct equates to more losses- an increase in noise and possible draughts because of the higher air speed (careful placement and selection of the outlets in rooms to minimise these effects are important). I will be trying to select and use a 90mm semi-rigid duct (outside diameter) or larger steel duct. I want to avoid the use of the 75mm duct and all its permutations such as each room being supplied with two 75mm ducts in parallel.
Larger ducts need mufflers or silencers as room noise can travel between rooms . If one has an attic or one can find a way to install the 125mm steel duct with insulation in particular routes the larger ducts may be the best way to go.
Be aware that installing a false ceiling can double the cost of the HRV. I will review all possible systems of ducts . If one uses steel I have been advised that one needs to insulate these as it can take a long time to heat up if the temperature drops leading to colder air being supplied for the initial start up.
The flexible ducts have multiple accessories to connect each part and extra cost is associated with this. The weaknesses of extra connections affects reliability. I will try and simplify the system of connections (somehow).
Ducts need to be cleaned (design and plan for this)
Keep the duct lengths short and straight to minimise losses.
Use large radius bends rather than 90 degree bends.
Consider placing ducts in the foundation when building new.
Some plastic ducts are antistatic (minimises dust collection on inside)
Some plastic ducts have antibacterial liners
Some plastic ducts are odourless and use physiologically and toxicologically safe polyethylene.
Some plastic ducts are smoother on the inside than others (minimises losses and reduces noise).
The non monetary factors for using a centralised Heat Recovery System that I can think of are:
■ comfort (help to filter diesel particles , pollen, outside smog etc from the forced incoming air)
■ building protection and health/hygiene (remove high level of moisture from cooking, showers, baths, and people that could damage the fabric of the building, CO2 from persons in the house and VOC (chemicals from furniture, beds, floor carpets, paints, plastics etc) and supply enough oxygen to get a good nights sleep. Reduced noise because windows do not need to be left open and no holes exist in the outer walls of bedrooms.
■ security (can keep windows closed)
■ thermal energy efficiency (recover up to 90% of the heat energy leaving the building)
I want to see if I can design the HRV with the 150/125mm steel ducts or use the 90mm polyethylene outside diameter ducts with the antibacterial liner, antistatic liner and low emission polyethylene.
Each of the polyethylene ducts return to either a supply manifold or extract manifold (see example below).
If I end up selecting the 150/125mm steel ducts these will use no manifold and the individual rooms are tapped into the main duct.
Extra Functionality Planned For the HRV
In order to get the most value from the centralised Heat Recovery Unit I plan to make a special cabinet to dry clothes using a feed and return air supply. I will add a heater to the cabinet to give the clothes a drying boost where necessary.
An interesting calculator I found is one that calculates the losses of ductwork and air speed. One can experiment using rectangular versus round ductwork and the inner roughness of the ductwork here. One can see the air speed change as one reduces the size of the ducts. There are another few options on the right hand side menu to calculate other factors.
Example of Duct Losses
Background Research and Notes
MVHR are not a fit-and-forget systems
Based on European CEN Standard 13779 ventilation for ‘medium’ air quality should be at least 10 L/s per occupant (15 L/s for high indoor air quality).-non residential
Ventilation rate of 8 l/s (30m3/h approximately) per person identified in CIBSE Guide A8
In order to achieve an air exchange of about 0.33 ach (air change per hour), one would have to open the windows wide for 5 to 10 minutes every three hours – even at night! –Source
Biggest complaints -noise and draughts (over dining area, bedroom areas etc) causing users to switch the HRV off.
Balance the air going in against going out-not practical to reach 0%. Aim for less than 10%-allowable imbalance between intake and exhaust air flow for these systems is 10%
Filters not changed can increase (double) the cost to run because the fans use more electric power to send air around.
Ensure that the HRV is accessible in order to change the filters.
A good strategy for the summer appears to be to reduce HRV speed/flow rate and open windows.
Total cost of HRV if left on appears to be around €60 for electricity and €60 for filters (Once a year). Check cost of replacement filters for own unit.
Ducts need to be cleaned every few years so the design needs to make it accessible.
A larger HRV unit than required can be more silent because it does not have to work near its full ventilation capacity.
A measured air noise level of less than< 24db for bedrooms (Finnish Guideline) . Can it be specified and delivered?
Noise levels up to 30 dB(A) were described as “too noisy” by more than 40 % of respondents. The standard for certified PassivHaus dwellings  is a limit of 25 dB(A) in both living rooms and bedrooms. Source
Maintaining indoor humidity below 7g/kg should help to reduce the risk of excess mite growth.
Note that air speeds greater than about 0.3 m·s–1 are probably unacceptable except in naturally ventilated buildings in summer when higher air speeds may be desirable for their cooling effect.CIBSE Guide A8
Significant problems were found with the commissioning of HRV systems, with only 16% of systems being found to have been commissioned correctly with respect to air flow and balancing. Source
44% of kitchens meeting the minimum requirement of 13 litres per second.Source
Measured air flow in 88% of systems utilising rigid ducting were equal to or greater than their design air flow values, whereas between only 40 and 44% of systems utilising flexible ducting met their respective design value. Source
Any leakage through the dwelling envelope will have an impact on the efficiency of the heat recovery component. Source
Lack of appropriate airtightness, lack of complete commissioning, poor air flow and extract rates (and associated lack of compliance with regulatory standards), lack of balance and inappropriate duct types. Source
Wolfgang Feist@WolfgangFeist-You don’t believe this?The “trick” is:We have a F8 fine filter at the external air (“fresh air”) inlet, therefore supply air is very clean
In another technical paper the following was noted as the cause of excessive noise. The source of the document is here
Extract from document shown below
“The following list of issues are all taken from actual findings on investigations that have been reported. Issues that can lead to excessive noise for occupants are noted under the following headings of design, installation, commissioning and maintenance.
• Centralised MEV or MVHR unit located in inappropriate place for break out or structure borne noise, e.g. bedroom cupboard or on rafters in loft above a bedroom.
• Poor ductwork layout – too many bends can lead to additional fan pressure requirement and regenerated noise
• Specification of flexible ductwork
• Inadequate attenuation of duct borne noise
• Installation issues
• Ductwork kinked or damaged inhibiting flow
• Ducts not connected up to supply or extract valves (which will inhibit flow and require higher fan setting)
• Wrong type of outlet fitted (using extract outlets for supply air can lead to regenerated noise)
• No anti-vibration mounts used
• Failure to ensure ductwork is clean when installed prior to commissioning
• Use of flexible ductwork where not specified”
I note the above is summarised at the recent passive house conference (see below).