Introduction to Fluid Cooling Towers : 2. Cooling Tower Types

 Induced Draft Counterflow:

• Fans pull air across the fill material.

• Air and water flow in opposite directions, maximizing contact time and heat transfer.

Other Types of Fluid Coolers:

• Natural Draft: No fans; air flows naturally.

• Force Draft: Fans push air across the fill material (opposite of induced draft).

Evaporative Condenser:

• Similar to a fluid cooler but contains a condenser coil within the tower.

• Water is sprayed over the coil, desuperheating refrigerant vapors, condensing them to a liquid, and subcooling within the tower.

• Uses evaporative cooling to cool the refrigerant.

Introduction to Fluid Cooling Towers : 1. Cooling Tower Components

 Heat Laden Water:

• Water from the condenser is discharged to the top of the fluid cooler.

• It passes through spray nozzles that atomize water into finer droplets before reaching the fill material.

Fill Material:

• Typically made of PVC or polypropylene (older cooling towers may use wood slats).

• Slows water movement and maximizes contact between air and water to promote evaporation and efficiency.

• Two types:

1. Splash fill: Breaks water into smaller droplets.

2. Film fill: Spreads water into a thin layer for enhanced evaporation.

Drift Eliminators:

• Designed to remove water droplets from discharged air, reducing water loss.

• Air and water droplets change direction, causing separation, and water is re-deposited into the tower.

Fans and Motors:

• Fans must handle large air volumes with minimal vibration and resist corrosion.

• Belt drive motors: Regularly inspect belts for wear or slippage. Adjust belt tension as needed.

• Variable speed motors: Allow energy savings by matching the fan speed to the heat load from the condenser.

Makeup Water Assembly:

• Freshwater line with a needle valve and float assembly maintains water levels.

• Manually check the float to ensure proper water flow, as mineral deposits can obstruct the needle valve.

Water Treatment:

• Use filtration technologies and chemical products to prevent toxins, biofilms, and fouling.

• Chlorine dioxide is commonly used to disinfect and prevent microorganism growth.

• pH levels should be between 6.5 and 7.

Cleaning and Blowdown:

• Clean cooling towers twice a year to prevent biofilms and remove solids.

• Blowdown removes solids from the basin, preventing clogging in the condenser tubes.

• Blowdown should account for 5-10% of the makeup water flow rate.

Introduction to Fluid Cooling Towers : 0. Introduction

 Fluid Coolers Overview - Notes

• Definition: Fluid coolers (also called cooling towers) are heat exchangers where air and water interact to reduce water temperature for reuse.

• Process:

• Hot water from industrial processes or HVAC systems is pumped into the cooling tower.

• Water enters at the top in a counterflow arrangement, meaning water and air move in opposite directions.

• Water is sprayed through spray nozzles into the fill material (PVC, polypropylene, or older wood slats).

• Fill Function: Slows water movement, allowing air to blow across. Induced draft cooling tower has fans pulling air across the fill material.

• Evaporation:

• As water passes through the fill, a small percentage evaporates (as little as 1%), absorbing heat from the remaining water.

• Cooled water returns to the condenser.

• Water can be cooled to within 7 degrees of the air’s wet bulb temperature. Humid air reduces efficiency, while dry air increases it.

• Water Loss:

• Water lost through evaporation is replenished via a fresh water inlet and float mechanism.

• Chemical treatment prevents algae and other organisms.

• Solids Accumulation:

• Solids accumulate from water evaporation, leaving minerals behind.

• Solids are removed through a blow-off pipe or manually to ensure efficient operation.

• Induced Draft Counterflow:

• Fans pull air, and air and water flow in opposite directions for maximum heat transfer.

Common HVAC Formulas : 5.2 Latent Heat Removal

 Latent Heat Removal:

• Involves removing moisture from the air (dehumidification), an essential function in climate control.

• Understanding latent heat removal helps in selecting appropriate dehumidifiers or air conditioning units.

Estimating Water Extraction:

• Latent heat removal is estimated by calculating the amount of water removed, measured in gallons per hour.

• Formula: Latent Heat Removal = Gallons of Water Removed × 8,830.

• 8,830: Derived from multiplying 8.33 pounds per gallon of water by 1060 BTUs (latent heat of condensation per pound of water).

Example:

• A dehumidifier removes 3 gallons of water per hour.

• Multiply 3 gallons by 8,830 to calculate the latent heat removed:

• 3 × 8,830 = 26,490 BTUs/hour of latent heat removed.

Real-World Application:

• Helps HVAC technicians design air conditioning systems and select equipment that efficiently manages humidity levels in residential and commercial spaces.

Common HVAC Formulas : 5.1 atent Heat

 Latent Heat:

• Related to dehumidification and moisture control in air conditioning.

• Important for achieving optimal humidity control, comfort, energy efficiency, and health.

Method 1: Using Total Heat and Sensible Heat:

• Formula: Latent Heat = Total Heat - Sensible Heat.

• Example:

• Total Heat = 25,000 BTUs/hour.

• Sensible Heat = 18,000 BTUs/hour.

• Latent Heat = 25,000 - 18,000 = 7,000 BTUs/hour.

• The system needs to remove 7,000 BTUs of latent heat per hour to control humidity.

Method 2: Using CFM and Grains of Moisture:

• Formula: Latent Heat = 0.68 × CFM × Delta G.

• 0.68: Constant (derived from air density and BTU conversion factors).

• Delta G: Difference in grains of moisture per pound of dry air (found using a psychometric chart).

• Example:

• CFM = 1000.

• Delta G (difference in grains of moisture) = 20 grains/pound.

• Latent Heat = 0.68 × 1000 × 20 = 13,600 BTUs/hour.

• The system needs to remove 13,600 BTUs of latent heat per hour for dehumidification.

Real-World Importance:

• Ensures comfortable humidity levels.

• Prevents fogged windows, reduces mold growth risk, and maintains a hygienic environment.

Common HVAC Formulas : 4. Sensible Heat

 Sensible Heat:

• Refers to the difference in heat content between the supply air and return air.

• It is the temperature change felt as air is warmed or cooled.

Formula for Sensible Heat:

• Formula: Sensible Heat = CFM × 1.08 × Delta T.

• 1.08: Constant for standard air (BTUs per pound of air).

• Delta T: Temperature difference between supply and return air.

Steps to Calculate Sensible Heat:

• Step 1: Obtain CFM value (e.g., 1200).

• Step 2: Measure supply and return air temperatures using a thermometer.

• Step 3: Subtract return air temperature from supply air temperature to find Delta T (e.g., 120°F - 70°F = 50°F).

• Step 4: Multiply CFM by 1.08 and Delta T (e.g., 1200 × 1.08 × 50 = 64,800 BTUs).

Real-World Applications:

• Ensures efficient system design and operation.

• Helps in troubleshooting HVAC systems.

• Important for maintaining occupant comfort.

Common HVAC Formulas : 3. Total Heat

 Total Heat:

• Sensible Heat: Heat causing a temperature change without changing the state of a substance.

• Latent Heat: Heat required or released to change the state of a substance without changing its temperature.

Psychometric Chart:

• Used to plot air conditions (dry bulb temperature, wet bulb temperature, and relative humidity) to determine enthalpy.

• Enthalpy represents the total energy in the air (both internal energy and the energy required for expansion/compression).

Delta H (Change in Heat):

• Calculated by subtracting the enthalpy values found on the chart.

• Example:

• Incoming air: 90°F at 40% humidity = 34.9 BTUs.

• Outgoing air: 55°F at 100% humidity = 23.2 BTUs.

• Delta H: 34.9 BTUs - 23.2 BTUs = 11.7 BTUs.

Total Heat Formula:

• Formula: Total Heat = CFM × 4.5 × Delta H.

• 4.5: Weight of air (0.075 pounds per cubic foot) × 60 minutes per hour.

• Example:

• CFM = 1200 (from previous lessons).

• Multiply 1200 by 4.5 = 5400.

• Multiply 5400 by Delta H (11.7) = 63,180 BTUs.

Importance of Total Heat Calculation:

• Crucial for system design, efficiency, and performance in HVAC.

• Helps HVAC technicians design, install, maintain, and optimize systems.