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Most existing tower blocks have poor ventilation and infiltration problems.

 

Most residents improve ventilation in their flats by opening windows which causes excessive heat loss and thermal discomfort.  Poorly ventilated flats suffer from poor indoor air quality with high humidity levels and high incidence of condensation and mould growth.

 

Although most internal toilets have  extract ventilation systems, they tend to be in poor condition and most flats have insufficiently ventilated kitchens.

 

An efficient ventilation system can ensure that the built-up indoor humidity, air pollution [including, carbon dioxide & carbon monoxide], biological contaminants and odour is expelled without losing the heat in the air.  The choice of ventilation systems will depend on the existing ventilation system, level of thermal insulation and airtightness.

 

REFURBISHMENT OPTIONS

 Basic

Improve airtightness

Provide controlled ventilation

Provide trickle vents

Good

Provide Heat recovery ventilation

 Exemplary

N/A

Typical air leakage in tower blocks

Improve Airtightness

 

Control of air infiltration is essential to assure indoor thermal comfort and to minimise energy consumption in tower blocks.

 

The quantity of air infiltration is determined by measuring the air leakage rate from the building envelope, which describes the relative tightness of a building.

 

Typical leakage rate is around 12 m3/h/m2 at 50 Pascal [Pa] pressure difference.

 

Airtightness test
A pressurisation test can determine air leakage in the building. The test should be carried out in accordance with CIBSE TM23. The process involves the building being pressurised to 50 Pa using a large blower fan. All external openings such as  doors  windows and extract fans/vents are sealed.

 

Once the leakage rate has been determined for the tower block, tracer gas measurements and infrared thermography can also be used to find the source of heat loss and leakage paths through the structure.

 

Mitigation

The Building Regulation Part L [2002] recommends  airtightness levels of building envelopes to be improved   to no worse than 10 m3/h/m2 at 50 Pa. The tower blocks should have airtightness target value of 5 m3/h/m2 at 50 Pa.

 

The following strategies could help meet airtightness levels:

  • Draught proofing of windows and doors

  • Sealing of external facade by overcladding

  • Adding sealants around window and door frames

  • Replacement of windows and doors with new airtight ones

Other considerations

 

Controllable vents

Care must be taken to ensure that controllable ventilators such as, air brick and trickle vents are not blocked.

 

Benefits

  • Improve indoor thermal comfort
  • Minimise energy consumption
Typical Cost

□  n/a

Funding opportunities:
□  n/a

Also see:

□  Provide controlled ventilation

□  Heat recovery ventilation

More information:

□  1Improving the habitability of large panel system dwellings, BRE, 1989

□  GPG 224 ‘Improving airtightness in existing
homes’, BRESCU

□  Residential Ventilation Association

Suppliers:

□  Chiltern International Fire

□  BSRIA

To register as a supplier click here...

 

 

Provide controlled ventilation

 

Once air infiltration has been been reduced, controlled ventilation must be provided to avoid risk of condensation, foul odour, high humidity levels, mould growth and poor air quality. 

 

Although windows can provide adequate ventilation for most parts of the flat, ventilation rates are highly variable, and heat recovery is very difficult2.
 

The main options for controlled ventilation are as follows:

  • Passive ventilation i.e., trickle vents

  • Spot ventilation i.e., extract fans

  • Balanced ventilation

Passive vents

Passive systems such as, trickle vents, stack ventilation and wind driven extract fans do not consume electrical energy.

Trickle vents, which are small adjustable ventilation openings could be provided whilst replacing windows.

 

In tower blocks, passive stack ventilation which uses the principle of rising warm air, may be impractical. However, double skin facades, where a layer of glass placed in front of a conventional façade, could be used to trap solar heat to preheat incoming air to individual flats.

 

Spot ventilation

Most tower blocks either have individual extract fans or have a communal extract system. Both these systems  provide spot ventilation to toilets. 

 

Extract systems should be provided with humidistat control to ensure that the built-up humidity is exhausted.

 

Balanced ventilation

These systems distribute outside air throughout the whole flat as well as exhaust stale indoor air.

The outside air is drawn in from a high level opening on the facade and ducted to living areas and bedrooms and similarly the indoor air is drawn from the kitchen and toilets  and is discarded through outlets.

 

Benefits

  • Improve indoor thermal comfort
  • Minimise energy consumption
Typical Cost

□  Trickle vents to existing window: £50/window

□  Spot ventilation: 550-650/flat

 

Funding opportunities:
□  n/a

Also see:

□  Provide controlled ventilation

□  Heat recovery ventilation

More information:

□  Oikos: Green Building Source

□  2Leeds metropolitan University

Suppliers:

□  www.airflow.co.uk

To register as a supplier click here...

 

 

Heat recovery ventilation

 

The heat from the outgoing air is transferred to the incoming air stream with the help of a heat exchanger without mixing the airstreams.

 

It can be provided as a part of a balanced ventilation system, or a spot heat recovery ventilator. These can be installed in places where a centralised system is unfeasible. They are most  particularly beneficial in kitchens.

This energy efficient ventilation system can recover up to 85% of the heat from the exhausted air.  Typically, in an air tight flat, the heat recovered annually by a heat exchanger system is proportional to the temperature difference between the inside and outside of the flat.

 

The efficiency of the heat exchanger depends on the type. The main types of heat exchangers are:

  • cross flow 70%

  • rotary wheel 80%

  • counterflow 90%

In most systems, the fan speed and supply air temperature can be adjusted to suit individual requirements.

 

Other considerations

 

Air tightness

The benefit of heat recovery ventilation will only be appreciable in flats that have low infiltration rate.

 

Noise

Noise and vibration generated by the heat exchangers need to be controlled thorough insulation and isolators. Noise should be low and constant without tonal characteristics.

 

Durability and maintenance

Although maintenance of the system largely depends on the usage pattern and effectiveness of the filters, the the air filters, supply and extract grills will need to be cleaned at least every quarter.

A clear operations and maintenance [O&M] manual must be provided to the residents

 

Benefits

  • Annual saving representing £40/ flat 3
  • Improve indoor thermal comfort
  • Minimise energy & CO2 consumption
Typical Cost

□ £1500/flat

Funding opportunities:
□  n/a

Also see:

□  Provide controlled ventilation

More information:

□  Residential Ventilation Association

□  3 Mechanical ventilation and heat recovery in high rise dwellings, BRECSU, 1993

Suppliers:

□  www.kiltox.co.uk

□  www.scanhome.ie

□  www.villavent.co.uk

To register as a supplier click here...

Project partners:           | Price Myers: Sustainability |Battle McCarthy | Architype | STBI | Franklin Andrews |            

           

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