Re: Relative humidity in highrise office building vs. outdoor relative humidity

[Guest guest]

Carol

If there is no air conditioning in the HVAC system for the office, or if the system is not set up correctly, the indoor Relative Humidity (RH) will be related to the outdoor level, but different if the temperature is different. If the HVAC system is oversized and set incorrectly, it will reduce the air temperature but increase the indoor RH, more so when the temperature indoors is much lower than the outdoor temperature.

Since comfort is driven more by the level of RH than it is by the air dry bulb temperature, the system should be set up and operated to remove moisture from the air. That is often not the case if the personnel involved are not well educated or if minimum first cost is the only concern.

You can often help conditions if you get a quality dehumidifier; note that cheaper units are often too noisy to use in an office. Make sure that you get the chance to try the unit out in your space and get one that is both quiet AND effective. Use the minimum speed setting that gives you the necessary comfort level (reduced symptoms). As a minimum you will want to use a dehumidifier that is Energuide rated; even those can be noisy so choose carefully.

My personal recommendations for those with your symptoms is to try for a maximum RH of 45%, although that is not always possible.

Jim H. White

Relative humidity in highrise office building vs. outdoor relative humidity

If the weather is humid should the relative humidity be the same inside an office building as it is outdoors? And what is considered "normal" RH in an office? is 50% RH too high for indoors? I have asthma and just started working in an office building that is pretty humid. Is there anything that can be done to lower the indoor RH? I am ready to ask to have the air vent in my office closed off. I think that might help a bit, don't you?

Thanks.

Carol

[Guest guest]

Carol:Relative humidity refers to how humid it is compared with the moisture holding ability of a given air mass.The warmer the temperature the greater the amount of moisture that can be contained as a vapor,so cooling the air can actually raise the relative humidity, even if the absolute humidity is lowered.Since most HVAC systems are designed to merely deliver supply air at a certain temperature,merely cooling the air with only limited dehumidification, which is very typical, will result in air that is cooler indoors,but with a higher relative humidity.Why do you think that disabling a portion of the local HVAC system will improve the situation? Life Energy Associateswww.LifeEnergyAssoc.com20 Darton StreetConcord, MA 01742To: iequality Sent: Thursday, August 23, 2012 12:35:12 PMSubject: Relative humidity in highrise office building vs. outdoor relative humidity

If the weather is humid should the relative humidity be the same inside an office building as it is outdoors? And what is considered "normal" RH in an office? is 50% RH too high for indoors? I have asthma and just started working in an office building that is pretty humid. Is there anything that can be done to lower the indoor RH? I am ready to ask to have the air vent in my office closed off. I think that might help a bit, don't you?

Thanks. Carol

[Guest guest]

Hi Carol, Ideally, RH within the space will be between 45% and 65% and as the cooling coils of air-handlers usually remove moisture from the air, we usually see the problem of the air being too-dry rather than too moist. Buildings in areas of low humidity usually have to have humidifiers installed to meet the minimum humidity requirements. When the building is in heating only mode, there is minimal moisture removal from the air and humidity levels within the space often rise to what we consider unacceptable levels. The occupants themselves may add to this rise through the simple act of breathing. We know that microbial growth escalates at over 70%RH, so it is always prudent to control RH to a level below this. As to shutting off the supply air register as a means of reducing RH - not a good idea and on a CV system the air that you throttle off has then to go somewhere else and this would necessitate an air balance for all of the registers on that system. In addition - the humidity is in vapour form, this means that it will pass through any porous material and distribute throughout the compartment (not just your office). It goes from a high pressure (atmospheric) area to a low pressure area - so shutting down your supply would likely reduce the pressure in your office and bring in more humidity. I would suggest that Step 1 would be to establish who pays for any assessment and remediation. In some instances this would fall upon your employer (if fitout related), the base building owner (if the HVAC system itself is faulty) or the complainant (yourself), if no issues of significance were identifiable. Step 2 should have investigation by a ventilation engineer who has understands IAQ and has the instrumentation to sample the subject space (your office). This would not only be for temperature and RH, but also CO2, dust, air circulation flow rates within the space, etc. They would also need to assess the air handling unit itself and identify the configuration and control of the system for that space. Some sampling should be logged and occur over at least a 24-hr mid-work week period. Step 3 is to make the changes suggested by the ventilation engineer. Step 4 is reassessment and verification that the issues have been addressed and hopefully, that you are satisfied. Regards,Ian ChildsNEW DIRECTIONS IN BUILDING SERVICES®www.ndibs.com.au www.fireassess.com.au P.(02)9594-4477 M.0414-472-042, or Childs M.0414-472-044