View Full Version : Humidity reccomendations in offices
back2space
22-10-2008, 03:43 AM
Guys
Quick question here since your all so good at what you do, thought would run this by you.
What is the recommneded levels for humidity in an office?
Our a/c in our office in Leeds comes through ducted chilled water units that provide heat/cooling to the workspace.
There is also a fresh air handler on the roof that circulates fresh tempered air at 18C through ducts in the false ceiling down into the workspace and into the toilets and other areas, an
extract system sucks air back out of the ceiling void through positive and negative pressures. (forget which one)
Tonight I brought in my digital thermometer as on nights were having problems with the temperature as in we feel chilly, as well as them not being able to turn the fresh air off due to no open windows we suffer from draughts from the fan coils being in 24/7 operation.
My digital thermometer in the space of 8hours has only changed from 23.4C to 23.5C suggesting a very very stable temperature but we feel chilly.
At my house the temps above would feel too warm but here they are a lot diff.
Having looked at the humidity were fluctuating between 30% & 31% which remains constant all night.
We suffer from dry eyes and sore throats due to such dry air.
Humidity at home is usually about 45- 50%.
In your opinion is 30% too low?
Kind regards
multisync
22-10-2008, 04:56 AM
30% is deemed low on the comfort zone.
These always get political so I could ask management for their input.
http://www.dfpni.gov.uk/ohs_info_sheet_5.pdf
Humidity
Humidity is the concentration of water vapour in the air and is usually expressed as relative humidity, measured as a percentage of the moisture that would completely saturate air at the existing temperature. It has little effect on thermal comfort at ordinary room temperatures, but extremes are to be avoided. While no specific standards are prescribed by law, the ideal relative humidity (RH) of air for comfort is in the range 55 - 65 per cent, though the range of 40 - 70 per cent is usually
considered acceptable. Above and below these limits there appears to be an increased tendency to ill-effects. The symptoms of low RH, ie a dry atmosphere, are mostly due to the effects on the mucous membranes of the nose, eyes and throat. Exceptionally high RH, ie very moist (above 70 per cent), causes discomfort as heat controlled by sweating is impaired. Such humid conditions can lead to excessive mould growth on walls, stored goods and documents and once the mould has grown, there is a potential for mould spores which can in some cases cause problems.
In buildings with mechanical ventilation systems (air conditioning) artificial humidity is often provided by water spray or (preferably) by steam humidifiers. While increased humidification, especially during the use of artificial heating systems, will reduce the number of complaints associated with dry air and, in some instances complaints associated with exposure to static electricity, its installation, use and subsequent maintenance has to be carefully monitored by a competent person to ensure the avoidance of contamination by micro-organisms which may result
in outbreaks of humidifier fever.
Multisync
London
What is your chilled water temperature?
What is your supply air temperature (measured close to the chilled water coil)?
The colder the coil, the more moisture it will remove from the air. Supply air below 12.5C/55F will dry out the building.
Is there some reason to run the fresh air system at night?
How cold does the outdoor air get at night?
The colder the outdoor air, the less moisture it contains. When the outdoor temperature drops below 12.5C/55F, that air will dry out the building. Tempering that air to 18C/64.5F does not add moisture to it.
back2space
22-10-2008, 05:45 AM
Hi guys! QUick responses so far.
THe reason the fresh air is operated 24.7 and at night is because we are nightworker, the building wouild be too sealed, (no opening windows) so fresh air is needed all the time.
Current outside air temp is 4C but throuhout summer it is the same here as the main a/c now just fired up it is now dropping away again, 28% humidity now!!!
Not sure on how cold the chilled water is I think I was told 7C. However this building during the day has about 300ppl working in it in different areas, on a night the fan coils to the office areas that are not occupied are shut down and fresh air to those areas also shut down.
Our office area is a secure room and the fan coils and fresh air are left on my guess at this time of year though is that they are calling for heat rather than cooling however I think we can feel the fresh air ducts at 18C (which doesnt come through the fan coils completly separate).
We are told that they specifiy the humidity level of the fresh air supply and it humidifies it if needed.
back2space
22-10-2008, 05:56 AM
Just to point out on a night there are only max 3 people working in the secure area whereas this room seats 60 people during the day.
multisync
22-10-2008, 06:23 AM
Quite possible there is a fault with the humidification. I would ask the facilities manager for his input after showing him the 28% reading
Multisync
London
We are told that they specifiy the humidity level of the fresh air supply and it humidifies it if needed.
I'm wondering what humidity they are specifying for the fresh air. Air at 18C/70%RH when warmed to 23.5C will be at 50%RH. If they are specifying less than this, the fresh air will dry out the building.
back2space
22-10-2008, 06:56 AM
Gary
The air is currently being taken into the building at 6C and heated upto 18C they specify it to be 45% humidity at the air handler.
It is then distributed around the building.
Gary
The air is currently being taken into the building at 6C and heated upto 18C they specify it to be 45% humidity at the air handler.
It is then distributed around the building.
Air at 18C/45%RH when warmed to 23.5C is at 25%RH.
back2space
22-10-2008, 07:11 AM
That seems like what is happening then! The 29% is whats getting added on from the people sat in here.
If they increase the spec to 18C/70%RH, that should do the trick. Let us know how it works out.
On the main A/C, ideally the temperature of the air leaving the chilled water coil should be about 12.5C to avoid excessive dehumidification. This may require raising the chilled water temperature.
back2space
22-10-2008, 07:38 AM
Perhaps I am wrong regarding the chilled water temp for the fan coil units, it is comfort cooling and perhaps it is about that temperature. The air isnt icy cold from the fan coils as you would get with a refrigeration system.
I think it is about 11-12C
However please note on a nighttime and with it being cold on a night now, the fan coils are not running in cooling and are demandning heat. Only the fresh air system is outputting cooler air but this has been heated up from the outside air. But i imagine it is still dehumidifying at the same time.
Heating air does not add or remove moisture... but it does lower the RH.
Relative humidity is the amount of moisture held in the air relative to the amount of moisture it is capable of holding.
RH is changed by either changing the moisture content of the air or by changing the air's moisture holding ability.
When air is heated, it is capable of holding more moisture, therefore (without changing the moisture content) its RH drops.
Cold outdoor air, when heated to room temperature, is very dry air.
back2space
22-10-2008, 07:55 AM
Yes i know they add water to the air via steam or something like that.
2007eng
22-10-2008, 04:00 PM
Quick question here since your all so good at what you do, thought would run this by you.
What is the recommneded levels for humidity in an office?
55%
back2space
22-10-2008, 08:31 PM
HMMM they are not achieving that at all!
In fact this is a reply to my email i got today off the FM.
The FM has got a quote to rectify all issues in the MPIC area on an evening, once he returns from leave he will approve the quote and the work will be done.
Kind Regards
Not really response I was looking for, im starting up with a really dry sore throat now. And gotta go into work tonight.
multisync
22-10-2008, 10:06 PM
HMMM they are not achieving that at all!
In fact this is a reply to my email i got today off the FM.
The FM has got a quote to rectify all issues in the MPIC area on an evening, once he returns from leave he will approve the quote and the work will be done.
Kind Regards
Not really response I was looking for, im starting up with a really dry sore throat now. And gotta go into work tonight.
Just put a bucket of water on your desk..don't go all whimpy on us
Multisync
London
TRASH101
22-10-2008, 10:17 PM
The easy answer is to set the temp for 16c and the rh will shoot up you'll work harder so you keep warm the companies productivity increases and becomes more competetive and eventually turns the recession into a boom.:D:D
back2space
22-10-2008, 10:18 PM
I know but its a helpdesk so we are on the phone all night! When your voice goes its hard to talk isnt it!
I was thinking of doing some sort of cabaret and running round with a water spray misting the air !!!
HAHA
TRASH101
22-10-2008, 10:21 PM
know but its a helpdesk so we are on the phone all night! When your voice goes its hard to talk isnt it!
I was thinking of doing some sort of cabaret and running round with a water spray misting the air !!!
HAHA
Don't laugh because that would work especially if you have carpets that you can "moisten"
back2space
22-10-2008, 10:23 PM
There is that solution or I could bring all my washing in and start drying it!
I got soaked the other night coming into work and my jacket was soaked, it was dry in a couple of hours!!!
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