relative humidity control by desiccant dehumidifier, 040607
TRANSCRIPT
Relative Humidity Control
Using
Desiccant Dehumidifier
By
Prof. Moustafa M. Elsayed
(consultant)[email protected]
Dehumidification by Cooling
Chilled water
Chilled brine
Direct expansion (DX)
Sensible and latent loads
Cooling dehumidifier (with Reheat)
Functional principle
Inge-95
Dry airair
Condensed water
CondenserAir heater
Expansion valveWater side
Cooling compressorGas side
EvaporatorAir cooler
Dehumidification By Desiccant
Dehumidification by Dessicant
Solid desiccant: silica gel, activated carbon, synthetic polymer, etc
Liquid desiccant: triethylene glycol, lithium chloride solution, calcium chloride solution, etc
Desiccant material
Examples of desiccant material
Adsorption: collect water as a sponge, example silica gel
Absorption: collection of water causes a chemical or physical change in the desiccant, example liquid desiccants
Characteristics of desiccant materials
Dehumidification by Dessicant
Low surface vapor pressure when dry
High moisture capacity (upto 10000 percent of dry weight)
Low mass (low heat capacity)
Dehumidification by Dessicant
Methods of dehumidification
Inge-95
40°C
30°C
20°C
10°C
0°C
-10°C
30%
50%70%
100%
5 g/kg 15 g/kg
tdry =
t wet
Sorption
Cooling
Dew-point temp.
Condenser Evaporator
Evaporating temp.
Cooling versus Sorption
Cooling and desiccant-based dehumidification systems are most economical when used together
The difference in the cost of electrical power and thermal energy will determine the optimum mix of desiccant to cooling-based dehumidification in a given situation
Cooling-based dehumidification systems are more economical than desiccants at high air temperatures and moisture levels
Desiccants are especially efficient when drying air to create low relative humidities, and cooling-based dehumidification is very efficient when drying air tosaturated air conditions
Cooling Versus Desiccant
Expense Comparison
Condensation versus Sorption
40°C
30°C
20°C
10°C
0°C
-10°C
30%
50%
70%
100%
5 g/kg 15 g/kg
t dry =Investment-expenses and
capacities are comparable!
Lower running costs
for condensation.
Inge-95
t våt
1 - 2: sorption
2 - 3: desorption, heating
of desiccant
3 - 1: cooling of desiccant
Desiccant Cycle
Temperature rise during dehumidification
process
Temperature rise is directly proportional to the
amount of moisture removed from the air
The drier the air leaves the humidifier the
warmer it will be (Constant enthalpy
process)
Comparison with dehumidification by cooling
coil
Desiccant Cycle
Desiccant Dehumidification System Alternatives
100 % Recirculation
X % Outdoor Air without Cooling
Desiccant Dehumidification System Alternatives
X % Outdoor Air with Pre-Cooling
Desiccant Dehumidification System Alternatives
X % Outdoor with After Cooling
Desiccant Dehumidification System Alternatives
X % Outdoor with After Cooling & Pre-Cooling
Desiccant Dehumidification System Alternatives
Methods of Desiccant Dehumidification
Methods of Desiccant Dehumidification
Pre-cooling + dehumidification:AC+CB
Pre-cooling + dehumidification + after cooling: AC+CE+EB
Dehumidification + after cooling:AD+DE
Applications
Removal of water vapor
Removal of volatile organic compound (VOC) molecules
Preventing the growth of mold, mildew, and bacteria by keeping the building dry
Applications (where airborn microorganisms can cause costly problems)
Hospitals
Medical Facilities
Pharmaceutical
Biomedical manufacturing facilities
Food & Confectionery
Pharmaceutical
Defense Systems
Condensation: A surface will not have condensation
on it if the air in contact with it has a dewpoint lower
than the surface temperature.
X < ºC dp X >ºC dp
X < ºC dpX >ºC dp
Ice formation: A surface will not have ice formation
on it if the air in contact with it has a dewpoint lower
than the surface temperature.
ϕϕϕϕ < 50%RH
Bacteria: Bacteria needs humidity to survive and
multiply.
Most bacteria will not find a suitable environment if the
Relative humidity is kept below 50%RH.
ϕϕϕϕ > 50%RH
Dehumidifying Heating
Drying out buildings: Heating will only move the
moisture to another part of the building.
With sorption dehumidifying , the moisture is removed.
Corrosion: Iron and steel doesn’t rust if the air over
the surface has a relative humidity below 50%RH.
ϕϕϕϕ < 50%RH ϕϕϕϕ > 50%RH
Handling of hygroscopic material:The quality of dry drugs, dry food, hard candy and
other hygroscopic material can only be maintained if
the relative humidity is kept below a certain level.
ϕϕϕϕ > 50%RHϕϕϕϕ < 50%RH
Electronics: The characteristics of electronic products are
changed at a high relative humidity.
ϕϕϕϕ < 50%RH ϕϕϕϕ > 50%RH
Mould: Mould and fungus formation is prevented if
the surrounding air is kept below 70%RH.
ϕϕϕϕ < 70%RHϕϕϕϕ > 70%RH
Odours: Bad smell will be drastically reduced if the
relative humidity is kept below 50%RH.
ϕϕϕϕ < 50%RH ϕϕϕϕ > 50%RH
No dehumidifyingDehumidifying
Product drying: When drying products a low relative
humidity is essential for a fast process.
Freezers problems with moisture
Frost build up on evaporators
Short periods between stops for defrosting
Conveyors can lock up by ice
Increasing temperature due to ice built up
Snow or frost on the product
Freezer solution with overpressure
Freezer alternative solution with dry air to the airlocks
■■■■ Merits of honeycomb structure
Extremely low pressure loss
There are many small openings in the section of honeycomb. Therefore, air
can pass through very smoothly without getting excess load and, thus,
unnecessary energy does not consume.
Extremely large surface area
With the special structure of laminated layers consisting of flat & corrugated
materials, the surface area to be directly contacted with the air is greatly
enlarged. Therefore, the capacity can be enhanced up to the maximum level
with the minimum space required.
Light, yet strong
The combined structure with the corrugated material being inserted between
the flat materials is very light but physically very strong and highly durable.
HONEYSAVEHONEYSAVE
Moisture ratio
H2O Dry material
The weight of H2O
The weight of dry material
1 kg 10 kg
= Moisture ratio
ex. 1/10=0,1 i.e. 10% Moisture ratio
Moisture loads
Inge-95
unintentional
Intentional
Moisture load,
water surfaces
Moisture load
Moisture load
from people
Diffusion
Moisture load
Combustion
1 Unintended ventilation
2 Intentional ventilation
2 water surfaces
4 Moisture load from people
5 Diffusion from material
6 Moisture load from material
7 Moisture load combustion
Selecting Design Conditions
Outside conditions, set 1: conditions immediately
surrounding the controlled space
Outside conditions, set 2: conditions of fresh air for
ventilation of the controlled space
Note: dew point temperature is more important than
dbt & wbt for moisture load
Relative humidity for storage and production
Type of Product RH Type of Product RH
Sugar Storage 20-35% Laboratory electronics 45-60%
Breweries 35-45% Plastic Pallets 5-30%
Coffee Powder 30-40% Computer peripherals 50-60%
Milk Powder Storage 20-35% Rust Resistance Below 40%
Seed Storage 35-45% Medical Syrups 30-40%
Unpacked Medicine 20-35% Capsule Storage 30-45%
Anti-Fungus 45-55% Powder Storage 30-45%
Camera Lenses 40-55% Wood Drying 25-35%
HT Switch Room 45-55% Explosive *35-50%
Transformer winding 15-30% Hospital Electronics 45-65%
Semiconductors 30-50% Normal Storage 50-55%
Archive 40-55% Musical Instrument 45-55%
Paper Storage 35-45% Leather Product 40-55%
Rust Preventionbelow 55%,
>40% for zero rustCable Wrapping 15-25%
Library 50-55% Chemical Lab 30-45%
Spray Paint 30-50% Harddisk Production 40-50%
Lithium Battery Below 2 % Magnetic Tapes 40-55%
Note: * Explosive storage must not be less than 30% RH as static electricity may build up and
cause sparks in the air to cause an explosion.
Using
Design Of Dehumidification System
HOW MUCH 4 PROGRAM
Introduction to How Much 4
Room calculation:On this page you can determine moisture load and what dry air condition the dehumidifier has to perform.
The page is divided in two parts. The first part is to sum
up the different moisture loads. After that it make a
approximate choice of a dehumidifier and type of installation .
The final answer is process air inlet conditions to the unit
and what moisture content the dehumidifier has to have
in the dry air to meet the moisture loads given
Offer data room calculation:This page is to determine running cost, to present a pay-off time and a present value of the investment .
Climate data is automatically taken from "Room calculation" which has to be filled in to use this page.
You can compare different solutions, when comparing
different solutions. When doing such a comparison the
most important figure is the present value of cost, which
is summing up investment and running cost
Air mixture calculation:This page offers an overview of an installation with a dehumidifier, it is not linked to any other page.
Follow the step by step instructions on the page
Air mixture calculation by-pass:Same as previous page but with the dehumidifier in a by-
pass airflow
Air mix ambient by-pass:Same as previous page but with the inlet from ambient
DR air mixture calculation:Same as "Air mixture calculation" page but with a
dehumidifier with a common inlet for both process and
regeneration air
DR air mixture calc. by-pass:Same as "Air mixture calculation by-pass" page but with
a dehumidifier with a common inlet for both process and
regeneration air
Review of Program
Online Access
Example
Calculate the dehumidification capacity of a
Room with the following data:
• Room Design Conditions (20 ºCDB& 20% RH)
• Ambient Design Conditions (41 ºCDB& 32% RH)
• Room Dimensions (13.5m length* 7.7 m width * 5.4 m
height)
• Concrete Building Type.
• Surrounded from 2-sides
• Air Lock Dimensions(2.2 m Length * 3 m width* 2.5 m
Height ) with 4 min/hour openings.
• Wind Speed 8 m/s.
• 16-persons work light in the test room.
Program Execution
Online Access