Richard Hollas from 21 Degrees explains why regular MVHR maintenance and servicing is essential, what it entails, and we accompany him step-by-step as he services a unit.

Interview with Richard Hollas

Richard Hollas, a commissioning and service engineer for 21 Degrees (formerly Green Building Store), details the process of servicing an MVHR unit, using Ben’s system as a case study. 21 Degrees supply a range of products and services for Passivhaus and low energy building projects. The team can take you through the whole process for MVHR systems; including the design, supply, installation, commissioning and servicing, and emphasise the importance of each step in this process.

There is a difference between MVHR maintenance and servicing

Richard starts by outlining the difference between the maintenance practices we can do as homeowners and the need for servicing by an engineer. MVHR maintenance should include changing filters every 6-9 months, cleaning air vents and possibly cleaning the heat exchanger every 2 years. An MVHR system should be serviced by a qualified engineer every 3-4 years to prevent issues like increased noise levels, condensation, and reduced airflow. A service will inspect the sensors and fans, remove any contamination, check air flow rates and make any adjustments to ensure the system is working efficiently.

Changing the extract filter in the kitchen

It should be easy to access your MVHR unit

Ben’s unit is in his garage and Richard explains that this is the case for about 20% of MVHR units. The best location is in a utility room or plant room with space around it. This means it’s always simple to maintain or service the machine. Putting an MVHR unit in a loft is not ideal because it will be out of the way. You also don’t want them to be in a bedroom or other main living space as there will be some low-level noise from their operation.

A service is also an opportunity to double-check the installation

Richard explains that during the first full MVHR service he will check that the unit has been installed correctly. A common problem that arises is that the Armaflex insulation has not been installed. This is an extra layer of insulation that goes over the ComfoPipe, which is required by regulation, and so would need to be added.

MVHR service: step by step

Richard uses Ben’s MVHR system as a case study to take us through the service process:

1. The initial system checks

Richard begins the service by looking at the status of the system in the installer menu. He checks to see if the fans are going at different speeds, which would indicate a blockage somewhere in the system. The fans on Ben’s system are working well. He then puts the system in service mode, which stops the fans, moves the bypass flaps to the right position to allow him to open the unit.

2. Examining the inside of the unit

With the front off, Richard uses his torch to examine the inside for contamination and notices that the sensors are dusty, but otherwise everything looks good.

Richard points out the bypass flaps, which are activated by the external temperature. At a certain temperature, these flaps come down, so that the air from outside doesn’t hit the heat exchanger and come straight into the house. As these are modulating ones, they will partially open and so allow the air to mix together. There is also a preheater for frost protection, if the temperature goes down to zero this will come on to stop the unit frosting up inside. The main box is the heat exchanger itself.

Alongside this is the circuit board, that is controlling the fans, bypass flaps and other elements, so it all works together. Richard needs to access the board to detach the preheater for inspection. The preheater can become clogged with insects, creating a blockage which will then affect the air flow. Even though the unit is sealed, sometimes contamination will occur. When changing your filters make sure the unit is on filter change mode, which turns the fans off to ensure that debris is not pulled off the filters into the machine.

Contamination on the extract fan

3. Cleaning the supply fan and extract fan

Although the supply fan will get a clean it’s usually in a really good condition already, whereas the extract fan will almost always have contamination. It is important to remove the extract fan for cleaning so that debris doesn’t drop into the bottom of the unit. Bottle brushes are ideal for cleaning the fan as most of it is dry flaky material that can easily be removed.

4. Testing the condensate drain

A small amount of water is put into the condensate drain to ensure it is draining freely. Moisture is coming into the unit from our day to day living and needs to travel through it, hit one side of the unit and then drain away. Water damage on one side of the unit would indicate a blockage.

5. Cleaning the sensors

Richard explains that the sensors are monitoring conditions, such as temperature and moisture and that it is really important to keep them clean. If they build up with dust they may give false readings (or even trigger an error message) which will affect the efficiency of the unit. For example, if the sensor that monitors external temperature is giving the wrong information it will affect how the bypass flaps are working and impact the preheater for frost protection.

The heat exchanger is removed and cleaned

6. Cleaning the heat exchanger

The heat exchanger is a box that the air flows through, so providing it is kept free of contamination it will keep working. A regular service will prevent a build up within the heat exchanger and ensure that it is easy to remove for cleaning.  Richard describes how a heat exchanger left for 5-10 years may become so contaminated that it is almost welded into place and won’t come out at all. If that happens a new unit will be needed.

7. Resetting the system

Once the fans and heat exchanger are clean they can be re-inserted, and everything can be plugged back into the circuit board. When the front cover is back on, the filters can be changed and the unit can then be switched back on. The first thing it will show is an error triangle as it carries out an analysis. Richard explains that it will check the bypass, the sensors and preheater to ensure it has been reconnected properly and that there are no faults. This will also happen any time the unit switched off and then on again.

Richard and Joe check an extract valve

8. Checking the air flow and vents

Richard checks all the vents for contamination around them and for excessive dust in the ducts. The air flows are also checked to ensure they are meeting building regulations. Richard is able to remove the vents and valves for cleaning without changing the original valve settings, as these have been set with locking nuts and are very difficult to change by accident. They should therefore be the same as when they were commissioned.

Bathroom extract fans often have the most contamination

The extract valves can get a build-up of contaminants in the kitchen from cooking and the bathroom from towels and skin but any contamination generally settles around the valves and doesn’t enter the ducting system. Richard has used a camera down ducting on several occasions to check for contamination and each time it just looks like brand new, as the filters are working to remove any bits before they reach the ducting.

Richard points out how the supply valves can have a ring of dust around them, but that it is not coming out of the vents. It is to do with the air pressure, as the air comes out of the vents and meets the air in the room the dust settles and this can easily be wiped off with a duster.

Richard uses an anemometer to check the air flows in each room to make sure the air flow is meeting building regulations. He can feel that the air flow is good and the readings show that Ben’s unit is achieving 50 cubic metres in the kitchen on speed 2, which is what it needs to achieve at speed 3. This shows that the unit is doing well and there is good ventilation.

Richard can also check his readings against the commissioned figures. If one valve is the same it is likely that they are all correct and with locking nuts in place there should never be a need to recommission them. If you didn’t have locking nuts in place and someone altered one valve, say from 5 mm to 10mm it would change the air flow and so affect all the other valves.

The extract valves are the most important ones when you’re measuring air flow during a service, because things could build up and potentially cause a blockage further down. This is unlikely to happen with the supply vents, because air comes through the filters first. If Richard doesn’t have the commissioning figures, then he will be looking to hit building regulations and make sure the system balances out.

MVHR can automatically deal with excessive humidity

Richard is sure that Ben will not have any problems with condensation as his Zender Q unit has a humidity protection setting, which will have been put on during commissioning. This means that if humidity reaches 75% in the house the fans will gradually speed up to remove the excess moisture automatically.

A service is an opportunity to recap information with the homeowner

Richard tells us how it can be hard for customers to take in all the information about their MVHR system at the start. They may just have had a heat pump fitted, under floor heating and a whole range of new products. He suggests having an MVHR service after the first 12 months, so everything can be checked and he can go through all the workings when it is less stressful. This develops a relationship and also gives homeowners the chance to ask questions.

Without regular servicing the unit may start to develop problems

When the service schedule is neglected it is likely that contaminants will build up. This could cause a conflict in the machine. For example, the fans might speed up to clear the air but this would then activate the noise guard, which is there to protect the house from noise. This would result in your fans slowing down again, and you may start to notice condensation. The unit is then not running at optimum efficiency and not performing well. It is much better to establish a regular maintenance and service programme to ensure your MVHR system works well for as long as possible.

Find out more

Visit the website of 21 Degrees

What makes a well designed MVHR system?

How do you specify high performance windows?

Two radical retrofits that use an internal wall insulation strategy

Low energy barn conversions

Transcript

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