Frequently Asked Questions

 --- ABOUT DEHUMIDIFICATION

This note is intended to assist users, decision makers and consultants, in addressing some of the more common questions and concerns related to use of dehumidification:

Q 1. How much moisture is in the air?
The air can hold enormous amounts of moisture, especially at higher temperatures. An average area of 100m sq, (1000 sq ft) could have 10 - 12 litres more than is desirable.

Q 2. Will a Dehumidifier prevent mould growth?
Yes. Mould growth appears on continually damp areas, especially on the cold side of a house where the sun doesn't reach. A dehumidifier will remove the moisture that is the root cause.

Q 3. Why do we have production problems only in summer?
Your particular products are probably sensitive to increased humidity. In the summer months, you have a higher relative humidity indoors than during the heating season, when it's usually very dry indoors. A system for dehumidification will keep humidity levels under control all year round.

Q 4. When packing products, We have a problem with water condensing in the package. Is there a simple way to avoid this?
This is common when packing cold products in a warmer environment, where the relative humidity, i.e. moisture content, is too high. This causes the moisture in the air to condensate on the product's cold surface.

1. Make sure the dew point of the air is below surface temperature of the product.

2. Or seal off the packaging equipment and supply it with dehumidified air

Q 5. When transporting powders, we have a persistent problem with sticking and caking. Why?
Powders are generally very hygroscopic, meaning they absorb moisture easily. A preferred solution is to lower the relative humidity in areas where the powder is processed

Q.6 How does a dehumidifier work?
The new range of Bry-Air Dehumidifiers are fluted media based and remove moisture through a process of continuous "physical adsorption".

The moisture is adsorbed in the dehumidification sector by the fluted, metal silicate desiccant synthesized rotor and is exhausted in the reactivation sector by a stream of hot air in the counter flow. Following the reactivation process, the adsorption sector is again ready to adsorb the moisture. Thus, the two processes of "moisture adsorption" and "reactivation" are taking place with separate airflows continuously and simultaneously. Positive sealing between chambers prevents mixing of the process and reactivation air stream.

Q.7 What is the range and capability of Desiccant Dehumidifiers and to what level can relative humidity (RH) be controlled by them ?
A. Bry-Air dehumidifiers incorporating desiccant synthesized rotor are available in a range of 170 cmh (100 cfm) to 40,000 cmh (24,000 cfm) as standard and engineered/packaged systems

B. As the dehumidifiers use desiccants, they work independent of apparatus dew point (ADP), and can continuously maintain relative humidity as low as 1% RH, even at subzero temperatures.

Q.8 Are the humidity levels, being specified, not easily achievable with regular air conditioning and refrigeration ?
Two items are significant in deciding the choice of the final equipment :
i) the amount of latent (moisture) load in relation to the total load.
ii) the relative humidity specified to be maintained
a) Generally, if the relative humidity is to be maintained between 50-60%, it is more economical and preferred to employ standard air conditioning. However, if the latent load, even at this RH levels, is predominant or significant, e.g. Supermarkets, large fresh air equipments, it is recommended and preferred to divide the sensible load on the refrigeration equipment and latent load on chemical dehumidification equipment.
b) For relative humidity to be maintained below 45 to 50%, desiccant dehumidifiers offer the most economical, efficient and simplest method of humidity control.
c) Often humidity levels are not correctly specified as the user is not aware as to what RH levels and moisture will have ill-effect on its products and processes.

Q.9 What are the limitations in controlling RH with central air-conditioning plants/window air conditioners?
In tropical areas like India, with normal central air conditioning plants, lowest relative humidity of 50%-60%, at best, are attainable economically, at room temperatures between 68oF to 75oF. This again is only possible with special design of the cooling coil and appropriate selection of the apparatus dew point and provision of sufficient reheat.
With window air-conditioners or split A/c units, in the absence of specially designed cooling coils and reheat provision, typical relative humidity of 60-70% are commonly experienced at times of high outside moisture ambient conditions like monsoon.
Removal of large water vapour/moisture through cooling requires after cooling to apparatus dew point close to freezing and substantial subsequent reheating, thus requiring both over sizing of the cooling equipment, as also increasing the operating cost with higher BHP per ton consumed, and reheat energy.

Q.10 How was low RH possible with A/C plants, prior to introduction of Desiccant Dehumidifiers?
Low RH requires very special methods for estimating moisture loads.
Once moisture loads are correctly quantified, to achieve low RH with air conditioning/ refrigeration, it is necessary to select a very low gas suction temperatures and accordingly design and select a cooling coil that will provide a low apparatus dew point of about 34 to 35oF. Considerable reheat has to be injected to maintain the desired room conditions by this approach. This method is quite cumbersome, uneconomical, complicated and requires very precise control approach to prevent coil freeze up. With this complicated method, if moisture was correctly estimated, relative humidity as low as 40% were being maintained, prior to the introduction of the rotary chemical dehumidifiers.
For even lower RH, designs were attempted by going further lower in suction temperatures, below freezing point, and freeze ups being prevented by continuously having to spray brine. This not only made the equipment more bulky and cumbersome but certainly very uneconomical to operate as it required tremendous amount of reheat and very high power consumption in terms of BHP per ton.
The aforementioned approach is a thing of the past and rarely employed today in the technically developed world.

Q.11 How is the dehumidification equipment sized?
To size the equipment, it is first necessary to correctly estimate the moisture load. At low humidity, water vapour will permeate at very significant rate and large quantity based on vapour pressure difference. As ASHRAE has not laid out moisture estimation procedures for low humidity requirements, most air conditioning engineers are not fully equipped to correctly estimate the moisture load. Estimation of the moisture load procedure is explained in a very easy to understand manner in the Bry-Air design and engineering data manual.
Once the moisture load has been correctly estimated the sizing of the dehumidifier is a relatively simpler task. Please see Bry-Air engineering data manual or call our nearest office for support.

Q.12 Is there any quick thumb rule applicable for determining the equipment selection ?
No. The moisture load in a particular area is directly influenced by :
a) The volume of the room
b) Outside absolute humidity
c) Inside absolute humidity to be maintained
d) The vapour pressure resulting from the difference between b) and c) above
e) The rate of migration of vapour resulting from d) above i.e. vapour pressure difference
f) Conveyor openings, if any
g) Door size and door openings per hour
h) Number of people and their activity level
i) The fresh air quantity all of which can significantly change the dehumidifier equipment selection for the same size room.

Q.13 Will the relative humidity being maintained inside an environment, with the help of dehumidifier, vary from season to season, depending upon the ambient temperature?
OR

What are the controls used to maintain the desired RH, when there is a wide variation in ambient temperatures and RH?
Like any refrigeration plant the load on the dehumidifier system varies due to ambient conditions. The temperature control is maintained by a thermostat. This RH control is achieved with the help of humidistat or a proportionate RH controller. There are several control option for optimizing dehumidifier equipment energy/performance by one or more of many methods like proportionate reactivation energy, switching on and off the reactivation energy, switching off the dehumidifier, switching off the rotary bed and the reactivation energy and keeping the air flows on, etc.

Q.14 Are higher size ducts required because the latent heat has been removed from the supply air?
This is not necessary as duct size is calculated on the basis of cfm of air. Any marginal increase in cfm can be absorbed in the standard higher sized ducts normally adopted.

Q.15 Are there any specific recommendations about building materials and paints to be used internally to reduce humidity ingress, particularly in areas where low humidity is to be maintained?
To prepare any space for humidity control, the choice of vapour barrier is based on the degree dryness or RH.
Commercial vapour barriers - moisture resistant construction material, paints and other coating offer a variety of design alternatives. Manufactures of vapour barrier materials can supply specific information on their products.
Additionally, Bry-Air has prepared a note on suggestions for vapour barrier treatment to control the permeation of water vapour to the minimum.
Between 40 - 50% RH, special vapour barrier paints will provide an economical reduction in moisture ingress. Below 35% RH, it is recommended to prepare the conditioned space properly with good vapour barrier treatment including polythene etc. as an inside envelope for reducing the moisture load which has a significant effect on the sizing of the equipment.

Q.16 Is the equipment fire safe, specially where inflammable or ignitable material is stored?
Dehumidifier equipment can be easily supplied with flameproof motors and controls to make it suitable for hazardous areas and flame proof/explosive proof applications. The Bry-Air Dehumidifier incorporates inflammable, i.e. ECODRY metal silicate desiccant synthesized rotor.

Q.17 Are there any reference/commendations from users regarding the satisfactory usage of dehumidifiers?
Yes, reference from various users of Bry-Air dehumidifiers are available.
The fact that we have thousands of Dehumidifiers operating in India and are producing this product in Malaysia also and exporting the same to Middle East, US Countries, South East Asia, including Taiwan, Hong Kong, Thailand, Indonesia, Singapore etc. and West Asia, serves as an adequate testimony to both the quality capability of Bry-Air Dehumidifiers.


Q.18 What are the common maintenance problems with dehumidifier? Are the spares and consumables available easily?
Bry-Air dehumidifiers are easy to maintain and do not require special skills either to operate or to maintain them. Elaborate maintenance manuals provide easy to follow instructions for installation, start-up and also a comprehensive trouble shooting guide.
Consumables and spares are easily available through any of the Representative, Regional or Branch offices located in all major cities in India and abroad.
Bry-Air also offers training programmes for service technicians, maintenance staff of user organisations, from time to time, to familiarise them with the operation and maintenance of the dehumidifier.