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Camfil Whitepaper - Energy Saving in Buildings Better AHU Pre Filters can bring substantial energy savings
1. WHITE PAPER
Energy Saving in Buildings
Better AHU Pre Filters can bring
substantial energy savings
From: Camfil Farr Ltd
Date: June 2010
2. Camfil Farr – Better AHU Pre‐filters Can Bring Substantial
Energy Savings
Executive Summary
It is generally accepted that using Low Energy Air Filters will minimise energy use for a given filter
particulate efficiency and air flow rate. This is achieved by the low pressure drop across the filter.
Another way the air filters can help save energy and maintain plant efficiency is by keeping coils and
other heat exchanger surfaces clean. The coils will then work to their full rated capacity.
The comparison of pressure drop reduction energy saving and energy changes involved in coil
efficiency reduction in this paper indicate that they are of a similar order and both significant. These
potential savings can be realised by using low energy air filters and to some extent by improving
heating and cooling controls. Other savings and benefits on maintenance costs and Air Quality can
also be made.
Introduction
This White Paper will show a way to assess the potential energy saving benefits of a maintained coil
and heat exchanger heat transfer efficiency, when fitting F7 class Low Energy Air filters as Air
Handling Unit pre‐filters. There has been limited testing and research into the energy saving benefits
of clean coils and the linked gain of using higher grade pre‐filters. Reduced variations in pressure
drop and coil heat transfer efficiency offer the prospect of tighter HVAC system control and
improved energy savings.
The Legislation concerning energy usage in Air Handling Units
Current legislation for energy inspections of Air Conditioning systems with Air Handling Units is
covered by the Energy Performance Buildings Directive. This requires an inspection and report which
includes the condition and effective function of the air filters. Energy saving measures such as the
upgrade of air filter systems with Low Energy Air Filters should be considered.
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3. The Business Challenge
The coming period will be difficult for energy managers and plant engineers running air conditioning
plants. The current budget constraints are being felt across the economy. The Carbon Reduction
Commitment (CRC) Energy Efficiency Scheme was launched in April 2010, impacting on an estimated
20,000 UK businesses. The CRC will no doubt bring the subject of energy consumption to
boardrooms across the country, with Indoor Air Quality and low energy consumption presented as a
business challenge requiring urgent resolution.
The good news is that it is a straightforward process selecting the correct air filters to ensure Indoor
Air Quality is maintained and energy consumption reduced. An Opportunity Assessment Survey
(OAS) or Air Handling Plant Assessment (AHPA) can be carried out to evaluate the potential for
improvement.
Better AHU Pre‐filters Can Bring Substantial Energy Savings
Some air filter manufacturers have for a long time advised the fitting of better pre‐filters to give an
energy efficient performance.
When using the Eurovent filter Life Cycle Costing model (LCC) Camfil advises fitting an Hiflo M7 F7
Low Energy Air Filter. For a 2‐stage filter system an Hiflo M7 F7+F7 set up is recommended.
EN13053 also states to AHU manufacturers that 'If a single stage of air filtration is used, a minimum
filter class of F7 shall be fitted'.
Traditionally' G3/G4 panels have been used as pre‐filters and indeed sometimes they are the only
AHU filters fitted. To be effective a pre‐filter stage should be positioned just upstream of the coils
and heat exchangers in the HVAC system. This gives increased protection to the AHU coils as well as
meeting recommended air quality requirements.
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4. The current Eurovent LCC model for air filters covers maintenance issues, which can arise due to
dust deposition; duct cleaning for example. However has consideration been given to the loss of coil
efficiency due to the deposition of fine dust layers on the heat transfer surfaces?
Studies on HVAC coil efficiency
Studies on HVAC coil efficiency and cleaning companies indicate even very thin dust layers on coils
can mean significantly more energy usage, eg. 0.3mm. depth results in a 10% increase.(see graph)
Let us now try to quantify and compare a. and b. below.
a) the energy usage and possible saving by using F7 pre‐filters to prevent coil heat transfer
efficiency loss due to dust deposition on heat transfer surfaces.
b) the energy saving that can be made on reduced air filter pressure drop using the Eurovent
LCC model for air filters.
(Note : In a. It is assumed that the HVAC control system would use energy to increase the
temperature difference of the heating hot water or reduce the temperature of the cooling chilled
water to compensate for the loss of coil efficiency, otherwise the system will not deliver the
required performance.)
To make a comparison we can adopt a building energy usage model. A recently published HVAC
model for air‐conditioned offices has been used for this purpose.
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6. Conclusions
The assumption has been made that all heat transfer losses have occurred through the cooling coils,
heating coils and air‐to‐air heat exchangers. In reality there will also be increased losses through the
pipe‐work system at places with poor or no insulation if temperature differentials are increased.
Although heat losses are not always lost to the building envelope leakage of heat must be regarded
as a very inefficient use of energy. Any loss of coil heat transfer efficiency must be made good by
increased input from the boiler in a heating system and the compressor in a cooling system if it is a
controlled environment.
There is no attempt to directly fix the upper and lower levels of savings that can be made by
maintaining clean coils with the optimising of air filters but there is clearly a strong link. The
comparison made is to try and establish a reasonable estimate of the scale of the energy saving
possibilities involved.
The upper level of 30% and lower of 10% for coil efficiency energy losses seem to be generally
accepted as the level of losses commonly encountered in HVAC systems that are at the upper and
lower ends of the plant condition and maintenance spectrum.
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9. Camfil low energy air filters are the solution. They offer the lowest air filter energy cost throughout
their installed lifetime.
For more information visit the Camfil Farr website www.camfilfarr.co.uk
Or subscribe to the Low Energy Air Filter Blog at www.lowenergyairfilter.co.uk
References
Save money and reduce carbon ‐ Commercial HVAC Nigel Lenegan – Low Carbon Consultant
Recommendation concerning calculating the Life Cycle Cost of Air Filters Jan 1999
EUROVENT/CECOMAF
Air Filters and LCC for F+S October 2002 Jan Gustavsson
EN13053 Ventilation for buildings ‐ Air handling units ‐ Ratings and performance for units,
components and sections
Clean coils equals efficient coils ‐ Feb 2010 Tom Fitzsimons
Study verifies coil cleaning saves energy ‐ Ross Montgomery ASHRAE Nov2006
Glossary of Acronyms:
AC Air Conditioning
AHPA Air Handling Plant Assessment
AHU Air Handling Unit
CIBSE Chartered Institute of Building Services Engineers
CRC Carbon Reduction Commitment
CLG Communities and Local Government
CO2 Carbon Dioxide
EN European Standard
EPBD Energy Performance Buildings Directive
Etracker Energy usage monitor and recorder
EU European Union
HVAC Heating Ventilation and Air Conditioning
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10. IAQ Indoor Air Quality
LCC Life Cycle Costing
kW Power rating kiloWatts (for AC Cooling capacity)
MEMU Mobile Energy Monitoring Unit
NOx Emissions of Oxides and Nitrogen
OAS Opportunity Assessment Survey
PM10 Particulate matter 10 microns and below in size
PM2.5 Particulate matter 2,5 microns and below in size
SBS Sick Building Syndrome
SOx Emissions of Oxides of Sulphur
TM Technical Memo (CIBSE)
VAV Variable Air Volume
VOC Volatile Organic Compound
UK United Kingdom
Contact information:
Camfil Ltd
Knowsley Road
Haslingden
Lancashire
BB4 4EG
Tel: 0044 (0)1706 238000
Fax: 0044 (0)1706 226736
E‐mail: filtersales@camfil.co.uk
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