Commercial Considerations

These will always colour the requirement for humidification. This can be paired down to two distinct camps, the cost or installation of the system and the cost of ownership. The two are not always the responsibility of the same organisation so there are two different criteria by which they are being judged.

A building owner-occupier will take recommendations from the building design consultant who will tailor the system to meet his client’s particular requirements. These could involve any one or a number of key criteria.

Health, Safety and Welfare of Occupancy

Keeping the work force comfortable leads to increased productivity but no definitive studies have been undertaken to quantify this. There are measures that can be applied but they tend to be negative rather than positive. Examples are: the number of complaints received regarding a specific condition such as drafts, sore eyes, dirty surfaces, static electric shocks. Also the number of sick days taken by the workforce compared to what is considered to be normal.

Initial cost of installation

We all want the best system at the lowest price. If the bill of quantities comes in too high the specification can suffer by down grading or deletion of equipment. This has the effect of retrofitting systems as part of the maintenance package based on the complaints received from the occupier.

Energy cost over the life of the plant and systems

This is becoming very current with the Climate Change Levy being translated into commercial incentives by the Department for Environment, Food and Rural Affairs (DEFRA) in conjunction with the Inland Revenue. The Enhanced Capital Allowance scheme offers the building owner the opportunity to reduce the first year costs based on energy efficient plant and systems being included within the building structure. This can be extended to include the energy bill as well as the maintenance and servicing costs covering the complete operation of the building over its predicted life span. The rules governing the Enhanced Capital Allowance Scheme are available on the ECA web site.

Flexibility for change of use

The occupants can change as well as the owners of the building. This could lead to different environmental requirements and hence extra cost. All these considerations will be designed into the system in the knowledge of the prevailing regulations and recommendations. Depending on the body we wish to base our design on, this will reflect the quality of the environment that workers will be exposed to.

To conclude, perceptions are our guiding force. The lack of regulation and appropriate policing means we must trade in Best Practice Recommendations. Health and safety of people will lead to increased productivity. A happy worker is a productive worker. We now enter the win/win scenario that can be attained without compromising our design integrity.

Humidification and its application within the air-conditioned building

This Masterclass will outline the basic issues of humidification, its application within the air conditioning system and identify the general range of equipment that is available. It also gives a comparison of the cost of ownership for the various types of systems utilised.

Why humidification?

Hygroscopic materials

Most people understand that materials expand and contract with a rise and fall in temperature but many do not understand that with hygroscopic materials there is a greater rate of expansion and contraction with a rise and fall in humidification level.  A dry atmosphere can cause textiles, carpet, wood, paper, leather, plastics, etc., to shrink, harden, crack, spoil and lose weight. Weight loss can be a particular problem when produce is sold by the kg.

Furniture, for example, would show the typical results of being in an atmosphere where the humidity has gone from the extremes of damp to extremes of dry. Panels could split and joints break. Interestingly, the joints of most items of wooden furniture are more susceptible to damage as the glue used to fix them is likely to be hygroscopic in its own right and more prone to failure than the actual material of construction.

Fig 1 – Hygroscopic Material

Comfort

In a dry atmosphere moisture migrates from the body through the nose, eyes, mouth and skin. Moisture migrating from the skin causes adiabatic cooling which will reduce the comfort of room occupants.

At 21ºC, with low humidity, moisture migrates from the skin making a room occupant feel cool. Raising the humidity level would reduce the ability of the moisture to migrate from the skin and the occupant would feel warmer.

The normal reaction, to combat the cooling effect, would be to increase the temperature of the space by one, two or three degrees. The amount of power required to produce the temperature rise can be greater than the power required bringing the humidity up to a reasonable level.

There have been instances where the temperature in a working environment has been reduced to nominally 19ºC and the humidity increased to 60%. The comfort level was considered acceptable and the power saving substantial.

Health

Volvic, the mineral water supplier produced a report in 1999, which suggests that an office with a humidity level of 25% would be as dry as the Sahara Desert.

Although it is acknowledged that low humidity is more uncomfortable than unhealthy, airborne bacteria can travel further and faster through a dry atmosphere than through a humid atmosphere. This may increase the possibility of contamination, in fact an ASHRAE report of 1979 states that `dryness causes cracking of nasal tissues which can give inhaled germs direct access to the blood-stream`.

Contact lenses

Contact lens wearers, particularly of the hard and gas permeable type, are often the first people to complain of a dry atmosphere. The lens sits on the eye on a film of moisture. Should this film dry out then the lens feels very coarse, little more than a piece of grit, which could cause permanent damage to the eye and result in the wearer having to wear the spectacles that they were trying to avoid in the first place.

Static electricity

Below 35%RH, static power will build-up in an object, which will discharge to earth through anything that comes into contact with it, this is normally the human body.

Walking over a nylon carpet, wearing man-made soled shoes could generate a static charge of 35,000 volts in a dry atmosphere. Raising the humidity would reduce the discharge to about 1,500 volts, less than 5%. Raising the humidity level above 35% allows all surfaces to become covered in a microscopic film of moisture that dissipates the static charge harmlessly to earth.

Walking over a nylon carpet could generate 35,000 volts

Fig 2 – Static

Psychrometric process

The psychrometric process of humidification should consider adiabatic systems, for example sprays, ultrasonic, wetted media and spinning disc, as well as isothermal systems which relate to steam, that is either local or centrally generation and would then be either atmospheric steam or pressurised. Both can be powered from electricity or gas.

NOTE: Our sincere thanks go to Mike Creamer of Business Edge Ltd. Re-creation of Drawings by Business Edge Ltd.

DISCLAIMER: Whilst every effort is made to ensure absolute accuracy, Business Edge Ltd. will not accept any responsibility or liability for direct or indirect losses arising from the use of the data contained in this series of articles.