Refurbishment opportunities for humidification

AHU
Adding cold-water atomising humidifiers to air-handling units can effectively provide free cooling.
Humidification is an increasingly important aspect of modern buildings. Lindsay Henderson considers how it can be added during refurbishment operations.The requirements of buildings and their occupants have changed dramatically over the past 20 years. The amount of equipment used has increased massively in the office environment. The heat gains within the office space due to more IT equipment are now far higher than previously experienced. Building occupiers are far more aware of their surrounding environment and, indeed, expect the indoor air quality to be controlled to the correct comfort conditions. Excellent opportunity The refurbishment and/or replacement of equipment that has come to the end of its life gives an excellent opportunity to incorporate humidification into upgrades of air -conditioning systems to improve the indoor environment, allowing health issues to be addressed, meeting equipment specifications and eliminating damaging and harmful electrostatic shocks — all of which are caused by dry air. Modern humidifiers offer various options for effectively introducing humidification into an existing building. Within the plant rooms of a building, space is often in demand. In many situations the high heat gains within the conditioned space necessitate air being supplied to the various floors of the building at a low temperature; in these cases the psychrometric conditions can restrict the type of humidifier that can be used to increase the moisture content of the supply air, and it is only possible to humidify using the isothermal process (i.e. steam humidifiers). Electric self-generating steam humidifiers cover a wide capacity range whilst still being very compact. Both types of electric self-generating steam humidifiers (electrode boiler and resistive) are very versatile and installation is straightforward. There is no need for steam humidifiers to be installed at the point of steam injection; they can easily be mounted on a wall or on a frame in an accessible area to allow good access for maintenance and servicing. The steam can then be run a short distance to the point of injection. Where it is not possible to inject the steam into the air-handling unit, typical in cases where humidifiers were not incorporated in the original system, the steam-distribution pipes can be installed into the ductwork with minimal disruption, giving more options where plant room space is a concern and allowing the possibility of humidifying into ductwork at floor level. Gas-fired self-generating steam humidifiers are also available. Again, they have a wide capacity range. Where large humidification duties are required, which is often the case when high volumes of fresh air are needed, high outputs are available from a single unit. Gas-fired Whilst the installation costs of gas-fired humidifiers are slightly higher than electric humidifiers due to the flueing requirements, as with electric self generating units they can be installed for steam injection into the AHU or ductwork, and outdoor versions are also available. If gas is available on site, all the benefits of steam humidification with the added benefits of energy efficiency and low running costs can be achieved, giving the investor an extremely short payback time — typically within 18 to 24 months. Incorporated into many old air-handling units are air washers. To ensure hygienic plant operation, regular and expensive chemical dosing is required. Due to this costly up-keep many air washers have long since been switched off. However, with today’s modern adiabatic humidifiers it is possible to minimise operating and maintenance costs while ensuring absolutely hygienic humidifier operation. Adiabatic cooling All cold-water humidifiers are adiabatic and cool the air. Where plant requirements have changed over time and high heat gains from the space have to be addressed, instead of increasing the fresh air volume and/or the cooling capacity of the system, adiabatic cooling can be used within the psychrometrics of the system and is effectively free cooling. The cold water humidifiers available in the market are atomisers, (spray and ultrasonic) and evaporative units. Unlike self-generating steam humidifiers, adiabatic systems can generally only be used in air-handling units or in enlarged ductwork plenum sections as the velocity of the air should not exceed 3.5 m/s. Ideally when replacing old inoperable air washers, the existing section within the air-handling unit should be used. The old recirculation pond can effectively be used as the drain section, and the installation costs are kept to a minimum. Minimise wastage Modern adiabatic humidifiers are designed to maximise the humidification efficiency and minimise water wastage. When looking at the whole-life costs of replacement and refurbishment within a building, cold-water humidification can offer very low running costs for large humidification loads — along with the benefits of free cooling. When looking at the replacement and refurbishment of buildings, humidification should be addressed to improve the indoor environment. All aspects of each application should be assessed, Cost, installation, energy efficiency and the whole-life costs of each system should be ascertained prior to selection and specification of what type of humidifier to use. Lindsey Henderson is director of the humidification division of Axair Climate Ltd, Talbert House, 52a Borough High Street, London SE1 1XN. LHenderson@axairclimate.co.uk
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