HVAC Heat Load Calculation for Humidification Plants – Step-by-Step Method
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- This guide explains the internal and external heat load factors, methods of calculation, and practical considerations used by engineers and technicians worldwide. Whether you are working in a spinning mill, industrial plant, or commercial facility, this method statement will help you perform precise heat load analysis.
- Accurate heat load calculation is critical in designing and operating a humidification plant. It ensures proper energy efficiency, stable temperature and humidity control, and cost-effective HVAC performance.
Heat Load
In order to determine the humidification power required for any department, the heat load of the department is to be found out. The heat load of the department can be broadly classified as Internally generated heat load and Transmitted heat load.
Internally generated heat load
The internally generated heat load is due to the heat liberated by the following ways:
- Driving motors
- Machinery's
- Compressors
- Pneumafils
- Overheat Cleaners
- Lighting Load
- Heating Lamps
- Persons working inside the Department
Transmitted heat load
- The Transmitted heat load is the heat that comes from Outside through the roof, walls, windows and doors as the outside Temperature is higher (Most of the period) than the inside department Temperature.
- The Heat load and the power required for the supply, exhaust and pumping system.
- The outside maximum Temperature prevailing during peak summer days.
The Transmitted heat load has been calculated for the department taking into account:
- The department size,
- The roof arrangement,
- Provision of false ceiling,
- Thickness of walls,
- Size of the doors and windows,
The Parameters for the heat load analysis are given in the following Tables.
Parameters for Heat Load Analysis with example:
| Parameters | (e.g.) Spinning Plant |
|---|---|
| Installed Motor KW | 341.0 |
| Lighting Load in KW | 0.36 |
| Number of Persons (day) | 12 |
| Department Size (m), | 189 x 103.5 |
| False Ceiling, | Yes |
| False Ceiling Height (m), | 14 |
| False Ceiling Insulation, | 4 |
| False Ceiling Thickness (mm), | Glass wool 25mm |
| Roof Type, | - |
| Roof Material | AC-sheet |
| Total Heat Load (k.cal./hr), | 2,45,000 |
| Supply Air Capacity Required (m 3/hr), | 85,000 |
| Supply Air Capacity Existing (m 3/hr), | 36,800 |
| Supply Air Capacity Existing (m 3/hr) inclu.WRS, | 82,000 |
Heat Load Analysis
- In This section, the pattern of heat in the various department of the mill has been analysed taking into account the heat generating sources inside the department and the transmitted heat that comes from outside through roof, walls, windows and doors.
- Based on the heat load analysis, the power required for the humidification system namely supply, pumping and exhaust are derived and compared with the existing humidification power.
Plant Motor Loading Analysis
In this section the loading based on actual power consumed by the supply air fan motors, Exhaust air fan motors and pump motors have been analysed.
Temperature and RH Pattern Analysis
In this section pattern of Temperature and RH existing in the ring spinning departments of the mill has been analysed.
Recommendation for Immediate Implementation
In this section various suggestions are given for immediate implementation to improve the operational efficiency of the existing humidification system.
Humidification Plant Details
- A Humidification Plant is a system that adds moisture (water vapor) to the air to maintain the right humidity level in a building or industrial area.
- The details of all the humidification plant namely, the HP of the fan motors, the speed and diameter of the fans and the HP of the pumps for e.g. Supply Air System
| Plant | (e.g.) Spinning Plant |
|---|---|
| Fan Range | 11 KW |
| Fan Dia (mm) | 1200 |
| Fan Blade | Adjustable |
| Fan Speed (RPM) | 1450 |
Air Washer Section
The Air Washer Section is a part of an HVAC or Humidification plant where air is cleaned and cooled using water spray.
📚Humidification System Design Explained | Air Washers, Direct Systems and Efficiency Tips
| Plant | (e.g.) Spinning Plant |
|---|---|
| Pump Range | 5.5 KW |
| Total Nozzle | 240 |
| Nozzle Type | Clamp-on |
| Nozzle Material | PVC |
Heat Load and Air Quantity
The air conditioning or humidification load is directly proportional to the total heat load in the department to be conditioned and the requirement of relative humidity to be maintained in the department.
The source of heat to the department are due to:
- External heat load
- Internal heat load
External Heat Sources:
- The heat load due to external sources is in the form of transmission of heat through walls, windows, etc. the other source is due to the solar radiation through the roof.
- The third source is the load due to the heat content of the infiltration of ambient air into the humidified department through doors, windows and other openings.
- External heat load sources is due to transmission and Radiation of solar heat and heat content of outside air infiltrating into the department through doors and other openings.
- The heat transmission through walls, windows, and Roof varies considerably from season to season and even during a day from morning, mid-day and evening.
- In general step should be taken to minimize the external heat load. Generally in the humidification for a textile industry the transmission due to the other sources like wall etc. are very minimum since brick walls offer a very good resistance for the heat transmission.
- However, glass has the peculiar property of transmitting radiation from high temperature source such and absorbing much of the radiation from low temperature sources such as the occupancy and other heat producing materials inside the building.
- Glass therefore acts as a one way valve for radiant heat. From air conditioning viewpoints this is undesirable in summer and hence it is advised that the departments may be constructed with minimum number of glass windows and ventilators.
- The rate at which radiation takes place depends on the temperature of the source and on the nature of the surface. Black, rough surfaces are good radiators and good absorbers.
- Polished, bright surface are poor radiators and also absorbers since they reflect most of the radiation energy which falls on them.
- Depending upon the transmission load and also the radiation load suitable materials can be selected for the roof of the building.
- Use of aluminium sheets is gaining importance these days for the roof since they reflect most of the radiation energy.
- The main source of external heat load since is coming from the roof through radiation required steps are to taken to minimize the same.
- Providing false ceiling to a great extent reduce the roof load transmitted to the department. Once the false ceiling is provided, the space between the roof and the false ceiling i.e. the attic space starts getting heated up due to the radiation heat of the roof.
- The heating takes place till such time an equilibrium temperature is maintained in the attic zone which known as the attic temperature.
- At equilibrium the amount of heat gained by the attic from the roof due to radiation is equal to the amount of heat transmitted the department through the false ceiling and the amount of heat let out into the atmosphere through the roof because of the difference in temperature.
- It is observed that the attic temperature in some occasion will rise up to 60°C.
- From the attic, as said above, the heat transfer takes place to the conditioned department and hence it is a source of heat for the air condition and so the same has to be minimized.
- Providing insulation to the false ceiling will increase the resistance to the transmitted into the department from the attic there by, the heat gained into the conditioned area is minimized.
- By providing ventilation to the attic it is possible to reduce the attic temperature but then the air draft in the attic may lead to fluff accumulation and power consumption for running the ventilation fan.
- The heat gained and the effect of false ceiling, insulation etc. can be analysed mathematically and the heat contribution to air conditioning load is worked out.
- Another source of external heat load is the load due to the heat content of the infiltration of ambient air into the humidified department through the doors, windows and other openings.
- Through this is a minor load, this may lead to hot packets. This can be minimized by keeping the conditioned area at a positive pressure so that the air entry will not take place and the department air alone will escape into the ambient. This will facilitate a well-balanced condition inside the department.
Internal Heat Source
- There are many heat source which are generating in the working department. In the textile industry the horse power of the machinery motors contributes to the internal load substantially say of the order of 50 to 70% of the total load the internal load department.
- The entire horse power installed for the machineries, when the machines are working is liberated in the form of frictional heat. Besided the inefficiency of the motors installed in the department will contribute to further heat load.
- To minimize the load due to the motors, it is advisable to size the motors depending upon the average load that is required for driving the machinery and also it is advisable to go in for high efficiency motors for the machineries in case the service factor is going to vary considerably in the case of ring frames etc. the other source which contributes to the internal load is the burning of lights.
- Though this contributes only marginally to the total load, the same is to be accounted at the time of the heat load sheet.
- In textile humidification, through the heat liberated by the persons working in the department does not contribute much to the load the same is also included at the time of making the heat load calculation.
- Once the total heat load is worked out, we may proceed to work out the capacity of humidification required for maintaining the required RH conditions inside the department.
- As discussed in the psychometrics, the level of RH required to be maintained in the department decided the dry bulb temperature inside the department with adiabatic saturation cooling process.
- The level of RH desired to be maintained in the department will in turn decide the quantum of saturated air to be discharged in to the department. More the RH desired to be maintained more will be the conditioned air to be discharged into the department.
- The 3rd factor that governs the quantity of conditioned air to be discharged into the department is the saturation efficiency of the air washer of the humidification systems.
The saturation efficiency has already been discussed in psychometrics. In short the formula that will gave the total quantity of conditioned air required is given by:
Conditioned air requirement
Q = T.H x 1.05 / 1.15 x 0.24 x DT
Where T.H is the total heat load
1.05 is a safety factor
1.15 Density of air in M.K.S units.
0.24 specific heat of air, DT temperature difference between the air washer leaving temperature and department temperature at the desired RH.
Basic factors for heat load estimation
Establish latitude of the textile mill location together with data of outside conditions.
- Summer: Maximum - dry bulb temp and relative humidity.
- Winter: Minimum - dry bulb temp and relative humidity.
- Find out the altitude, if the mill is located considerably above mean sea level.
Consider general particulars of the factory building such as:
- Type of building (Flat roof, North light)
- Material and thickness of construction of roof,
- False ceiling,
- Walls and orientation of the building.
- Any other departments adjacent to the one under consideration.
- Obtain the individual motor loads (KW or HP) of the various machines.
- Consider capacity of existing humidification plans, if any.
- Solar heat transmission through roof,
- Heat load from machines,
- Heat load due to light,
- Heat load due to persons inside the department.
Minimising of heat load and hence the quantity of the air conditioning load:
- As discussed above minimizing of heat load will result in low quantity of humidified air to be discharged into the department. This will result in reduced capital and running cost of humidification.
- Thus a designer should aim at minimizing the requirement of conditioned air by suitably designing the system.
It is possible to achieve reduction if one could specifically look into the following:
- Reducing the external heat load, internal heat load.
- Maximizing the saturation efficiency of the air washer.
- Reducing the heat pick up in the conveyor arrangements.
The reduction in the quantity of air due to the various factors can be worked out analytically.
Reducing the external heat load:
- It is possible to reduce the external heat load due to radiation transmission by providing roof cooling also the point that had already been discussed as above.
- Under deck insulation for roof can also be considered. It is also possible to reduce the internal load by opting for group drive within its limitations.
- In case it is possible to keep the drive motors of the machineries outside the conditioned area, the internal load can be minimized with regard to the designing of the conveyor arrangements like ducting etc., the same will be discussed in the subsequent paragraphs.
Conclusion
Proper heat load analysis allows HVAC engineers to optimize supply air systems, reduce energy costs, and improve indoor comfort. By considering machinery loads, lighting, human occupancy, and external heat transfer, you can achieve a more reliable and efficient humidification plant design.
📢 Share your experience in the comments what challenges have you faced while calculating heat load in humidification systems?
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