Humidity control of offices, call centres, museums is a problem when the buildings are served with ceiling mounted fan coil units. The reason is that the fan coils provide excellent temperature control to the areas they serve but in winter they do not add moisture to maintain a comfortable humidity level when the natural humidity is at its lowest. In the summer the cooling strips out moisture from the air making the environment uncomfortably dry.
Due to the nature of modern buildings the buildings are often vertually sealed to prevent energy losses escaping through energy expensive heated or cooled air escaping. The outside air into the building is at a minimum and the duct through which it travels, normally to the back of the fan coils is unheated and small in diametre making it an unsiutable place in which to inject moisture to ensure a comfortable humidity.
Many building experience the issue that this design of building creates. Low humdity levels experienced in winter and summer are well below the level accepted as adequate for general comfort and to prevent dry eyes, sore throats, headaches, respiratory problems, unpleasant static shocks and spread of viruses.
The main guidance from the Chartered Instuitute of Building Service Engineers (CIBSE), recommends humidity levels of 40-60 % rH for general comfort conditions. There is also the EU Directive on Display Screen Equipment which recommends humidity control for people working at computer workstations.
So, we have identified the problem of low humidity and people in the HR dept have recieved complaints of sore eyes, Health and safety are concerned about static levels and someone in the IT department has contacted their union. What is the Solution? What options do you have?
Well, the fact there is no mechanical air handling plant to install the humidifiers into, limits the type of humidifier suitable for use in this particular application. Any system which requires to be installed into the air distribution system of the building is therefore ruled out leaving.
Therefore other options have to be considered and as always there are pro’s and cons to each option but I do believe that one is the stand out solution.
The options to be considered are:
1. In room Steam Humidifiers
2. Ceiling Mounted Humidifiers
3. Direct air micro fine High pressure spray Humidifiers
Electrode or Resistive element steam generators
These electric humidifiers use electrodes or elements in a boiling vessel or cylinder to heat the water and produce steam for injection into the duct work or directly into the space via a room distribution fan. Controlability is good and output variable using a room sensor.
Picture: Electro Vap Electrode Boiler Steam Humidifer
The units would have to be installed within the space, on the wall or on the columns within the offices. Each unit requires a power supply, a water supply and drain suitable for water at 60C or higher to discharge. The units whilst not unsightly with the fan unit mounted within the humidifier look quite cumpbersome and bulky within a neat office space.
Electric Steam humidfiers are commonly used in many applications but in this application installation of power, water and drains within the office space is disruptive and often not easy to route the drain water that is just off boiling.
With power consumption being scrutenised within buildings even more, it is felt that the running costs of steam humidifiers the above installation reasons and the look of several units in a large space do not make this the ideal solution
Ceiling Mounted Humidifers
These humidifiers recirculate air through air intake and outlet grills in a ceiling. They pass air over a wetted media to pick up the moisture and humidify occordingly.
The units are installed above the ceiling and ideally require a depth of 300mm. The units are approximatley 1000mm square. Flexible ducts are required to be installed on the air inlet and outlet of the humidifiers running to grilles in the ceiling to allow for even distribution of the humidified air. Each unit requires a power, water and drain connection and free access to the underneath and side of the units for regular maintenance of the water tank, the filters and humidifier matrix.
Whilst ceiling mounted humidifiers are excellent in principle. In practice the space required for installation and effective maintenance is an issue and the small moisture lift provided by the evaporative humidifier means that alot of units are required making them inpractical for application where cooling is taking place.
Installation of the power, water and drains for each unit would not normally be an issue above a false ceiling however the fact that the control and monitoring of the units can not be done centrally and the set point has to be set on the units themselves is another downside.
In Room Airtec High Pressure spray humidifiers
The incoming water supply via a reverse osmosis system to prevent mineral dusting in the space and passes through a built in UV steriliser before going to the high efficiency water cooled high pressure pump.This provides water at 50 bar to humidification heads which incorporate a small fan and nozzle. The fan draws warm, dry air, directly from the office space past the nozzle which sprays finely atomised water, this process allows fast effective evaporation of the moisture directly humidifiying the space.
Picture: Airtec Hydro One office humidifier head
The heads are grouped in zones and are controlled by sensors which keep the relative humidity constant each area but supplied from one central valiable speed pump.
The UV steriliser, reverse osmosis plant and pump station can be mounted remotely from the humidifiers in a plantroom area. This allows for easy access for maintenance without disruption within the space. Nozzle heads are mounted on columns or walls within the space with the number of number of nozzles required dependant on the humidity duty for the space and to allow excellent distribution of humidity throughout the space. The water from the pump is supplied in high pressure hose above the celing run in a conduit along with the control and power cables for the humidifier heads. This means there is very little disruption within the space and only the nozzles head visible in the offices.
As the pump is a water lubricated hydraulic pump no maintenance is necessary. All main components of the system are stainless steel allowing for long life and no maintenence.
So by looking at these systems we can determine that the high pressure nozzle system offers the best solution to this type of application. The virtually silent operation of the heads, the good moisture distribution, zone control off one centrally located pump promote ease of installation which is all provided with an extremly low power requirement and threfore running cost (under 2kW for the whole building compared to 200kw for a steam humidifier). The low maintenance and spares requirements of the system and life span whole life cost of the system beat the other systems providing an attractive payback time for refurbished offices as well.
By humidifying directly into the space the true effect of the humidity will be felt on the floors eradicating the dry air issues.
It has been proven many times that once a building is effectivley humidified you can often reduce the temperature of the building to a more sensible level allowing large savings in running cost due to a decrease in temperature by a couple of degrees. Direct room spray humidifiers are also a beneift in the summer as the spray has a cooling effect, this has often been seen to reduce the load on the mechanical cooling required in the summer months. This all assists in reducing the environmental impact of the building and by adding this type of humidifier system you shall create a better environment and reduce the energy used and running costs of the building.