Steve Clarke MVHR Designer / Service Engineer Commissioning and Maintenance of MVHR Systems

Why do we have to commission MVHR systems? Optimise the efficiency of the heat recovery. Maximise the energy efficiency of the system. Deliver the required amount of air into / out of each room. Ensure controls are correctly set for the MVHR equipment, building and occupants. Ensure air transfer paths are sufficient. Ensure the system has been installed as designed, many are not ! Check for air leaks. Record all settings for future reference. Produce documentation for Building Control / Consultants

Why do we need ventilation ? 7l/s = 25.2m3/hr therefore ideally m3/hr/person

Air flow measuring Swema hot wire anemometer 7 to 450m3/h, a net of hot wires. Pros: very low pressure loss in the domestic range. measures air mass flow rate not just volume flow rate therefore more accurate at different temperatures. Cons: quite large measuring head. expensive at around £1,600. Best tool for commissioning

Air flow measuring Airflow LCA 301, moving vane with hood 100l/sec 360m 3 /hour. Pros: smaller so will fit awkward places easier. relatively cheap about £400 Cons: higher pressure loss. takes a while to run up to speed. susceptible to air jet causing false reading. Probably the best tool for maintenance checks.

Commissioning – air flows

Commissioning – recording settings

Supply or extract air valves fitted in the wrong locations, i.e. valves switched. Incorrect air valve mounting rings used or not properly secured. Air valves and external grills fitted in positions that make it very difficult to collect the air for commissioning. Air valves caulked in place (not possible to adjust). Intake and exhaust duct insulation missing or not properly installed. Wet seal not dry seal trap used on condensation outlet or no trap fitted at all (drain under negative pressure, wet trap could dry out in summer). Condensation outlet put through wall to outside (could freeze up). Frost protection pre-heater or supply duct heaters not properly wired up. Noisy air valves (especially relevant in bedrooms). Difficulties achieving desired boost air flows on flexible ducting systems. Common commissioning issues

Less Common…but have happened Ducts connected to the wrong ports on the MVHR unit, i.e. supply valves sucking, extract valves blowing ! Air leaks found on the ductwork system i.e. damaged flexible ducting or poor duct connections. Wrong handed unit used, duct ports switched. Frost protection pre-heater installed upside down. i.e. filter after the heater cassette. Inappropriate dampers used on extract system. Professional commissioning therefore advised as some of these issued would not necessarily have been identified. Less common issues

External grill locations Roof terminals make it impossible to measure the air flows externally to check for leaks. High level grills make it difficult to measure external air flows. MVHR units located in lofts therefore not ideal.

Air valve locations Please locate air valves in locations that are easy to access for air flow measuring purposes: o not too close to wall / ceiling corners o above shower rails o above kitchen cupboards o behind wardrobes

MVHR maintenance requirements Every 4 to 6 months: MVHR and kitchen extract filters to change however there are exceptions: - due to external conditions / events. - due to internal activity / cleanliness. External grills to check for blockages. Condensate drain to check for leaks. Periodically: Clean extract air valves – potentially dusty or greasy Cleaning of the extract ductwork, is this required ?

External event MVHR unit left running whilst paving was being cut and laid. Intake grill positioned quite low to the ground. Result – very fine dust particles penetrated through the intake filter into the heat exchanger. It is important to keep the MVHR systems turned off while the site or property is still dusty.

Intake grills What is wrong with the location of the intake grills in these two pictures ? And by the way what is that white insulated plastic pipe with a tundish ? Intake

Intake grills continued This is the intake grill from the previous slide after being in service for only 12 months. This is why it is not a good idea to have grills too low down especially with an insect mesh behind the louvres. Insects will end up in the MVHR unit intake filter but this is a serviceable component.

Internal event The occupier was in the habit of burning several large candles in the bathroom. Result after 6 weeks the extract filter was almost blocked with a thick waxy soot deposit. Better to be in the filter rather than lungs however ?

Set of dirty filters, about 1 year old Which is intake which is extract, why?

A final note on filters…. Central London intake filter Pre-occupancy building dust

Extract valves Extract air valve found in a kitchen in a 12 month old house. Flies and dust stuck to grease. The air valve also had a cone shaped filter behind it but this trapped the flies between the valve and the filter. A better solution would have been to fit a filtered kitchen extract grill with a visible filter.

More extract valves Bathroom extract valve after a few years in service. The dust is lint off towels etc. Possible to fit a cone shaped filter behind the valve to stop dust entering the ductwork however “out of sight” usually means “ out of mind” The filter will substantially reduce air flow when dirty and could be sucked further into the ducting system if not secured.

Yet more extract valves “Bunch of straws” damper in a plenum chamber behind the bathroom extract grill shown below. The grill is also partially blocked. A traditional adjustable circular extract valve would have been a better option. Dampers behind extract valves or grills is not to be recommended. Periodic checking and cleaning of extract valves is recommended.

Cleaning extract ductwork system ? Ductwork bend above a bathroom extract air valve, these can be cleaned with a damp cloth very easily. Extract fan blades after 4 years. If accessible these can be cleaned, however unless the fan is very dirty it is probably not cost effective, especially if the fans are difficult to access.

MVHR maintenance in summary Change the filters at regular intervals. Check the intake & exhaust grills for blockages or obstructions. Clean the extract air valves if necessary. Clean the ductwork behind the extract air valves if necessary. Maybe clean the fan blades if easily accessible.

For more information contact: Steve Clarke Designer / Services Engineer Green Building Store Tel: