Heating Ventilation and Air Conditioning Full Course - HVAC Course (Part 3)

 

HVAC - Modes of Heat Transfer

        This post is the third part of the complete Heating Ventilation and Air Conditioning. We will Study Heating Ventilation and Air Conditioning from Basic to Advance level. So, Let's Start..

Modes of Heat Transfer :

        Following are the three types of mode of Heat transfer.

* Conduction.

* Convection. and

* Radiation.

Conduction : It is the mode of heat transfer through solid materials.

Convection : It is the mode of heat transfer through liquid substances.

Radiation : It is the mode of heat transfer without any medium, for example, vacuum.

Enthalpy:

        It is the amount of inside energy and result of pressure and volume.. This sum "U+PV" is known as "Enthalpy (H)".

                            H = U + PV

(or) Heat content of a body is called as Enthalpy. The units of Enthalpy are kJ / hr, Btu / hr etc.

Humidity :

            The amount of moisture present in air or presence of moisture content in air.

Air : It is the mixture of various gases present in atmosphere.

Types of air : * Saturated Air & * Unsaturated Air.

Saturated Air : Air which is having 100% moisture present in it, is known as saturated air.

Unsaturated Air : Air in which moisture is present at standard normal condition, is known as unsaturated air.

Types of Humidity :

            * Relative Humidity (RH) : It is the ratio of amount of moisture present in sample of air to the amount of moisture present in saturated air. (or) It is the ratio of unsaturated air to saturated air with respect to the moisture at atmospheric conditions.

* Specific Humidity / Humidity ratio (w) : It is the amount of grains of moisture present in sample of air is called as specific humidity. The unit of specific humidity is Grains/ lb.

 Dew Point :

                It is the temperature at which buildup of condensation begins.

Condensation :

            Conversion of vapors to liquid is known as condensation. (or) Cooling of vapor (heat) to liquid form is known as condensation.

Evaporation : 

            Conversion of liquid to vapor is known as evaporation.

Air flow : 

            Here is HVAC industry airflow is measured in CFM (cubic feet per minute) or L/S (Liters per second) or CMH(Cubic meter per hour).

* CFM = 2118 m/s

* CFM = 2.118 L/s

* CFM = 1.8 x CMH

Following things has to be taken care during performing Air-conditioning. Temperature, Relative Humidity, Fresh Air, noise criteria (dB), Filters, etc.

Temperature :

            According to ASHRAE human comfort zone is 76 °F / ( 22 °C - 24 °C) / 24 °C.

Example, for Hyderabad --- 106 °F --- Removing Heat (cooling) --- 76 °F. 

similarly, for Delhi--- (-2 °C) --- Adding Heat (Heating) --- 24 °C. 

* Relative Humidity (RH) :

            Moderate relative humidity for human beings should be between 30 - 70%.

            Summer (50% RH)                 Winter ( 35% RH)

Example, For Mumbai (65% RH ) ---- Dehumidification (Removing of moisture) --- (50% RH)

Similarly, For Hyderabad (35% RH ) ---- Humidification (Adding of moisture) --- (50% RH)

* Fresh Air :

            According to ASHRAE 2004 - 62.1 edition,  fresh air 2009 62.1 edition, fresh air should be

IAQ / CFM = [(CFM / person) x (Number of people)] + (Area in sq ft x CFM per sq ft)

For example, 

                    =[(5 x 2)] + (200 x 0.06)

                    =10 + 12.00

Fresh Air / IAQ =  22 cfm.

Noise Criteria :

                It is a measure in terms of decibels (dB) or Hz. Noise criteria for the apartments or residential block is equal to 35 dB. Noise criteria for supermarkets is 45 dB, Noise criteria for commercial offices is 35 dB.

Filters :

            Filters are used to purify the the environmental air up to its maximum extent. i.e; up to 10 μ  filtration. Filters are of various types :

Bag filters, nylon filters, canvas filters, HEPA filters, Synthetic filters, Fibrous Filters (Material : coarse fibre coated with viscous adhesive for velocity 300 - 600 fpm.), 

HEPA filters:

                The acronym HEPA stands for High Efficiency Particulate Air filter. HEPA filters are generally used for high clean room applications like in hospitals, pharmacies, Research labs, operation theaters, etc.These are special type of filters which can purify air up to 99.99%.

 Project Requirement :

* Architectural Designing :

            With the help of architectural designs we get to know all the details regarding interior of the building, exterior of the building, such as plans, elevations (Front elevations, Back elevations, side elevations etc), details regarding doors and windows etc. All these details are very important while doing the heat load calculation in HVAC. Also, these details very much help us while designing the HVAC layouts.

* Structural Drawings / Civil Drawings:

            With the help of structural drawings we get to know, all the details from construction point of view. Such as constructional thickness of walls, material used to construct walls, and details of beams and columns, RCC- slabs, Foundation floors etc. These details help us in calculating the U-values which are required for heat load calculations in HVAC.

* Reflected Ceiling Plans (RCP) :

            With the help of Reflected Ceiling Plans, we get the details regarding fall ceilings, their constructional make, dimensions or the distance from floor to fall ceiling or from the roof. RCP's help us while routing the duct designing, it help us in knowing the available gap between the floor and the ceiling, so that we can manage to run our duct work in HVAC.

            Well, here finishes the third part of this full HVAC series. Stay tuned for more upcoming parts of this HVAC series. Till then, keep Learning, Keep Growing..

Access Previous parts of this course, if you have missed it, by clicking Below..

Part 1 -- Click Here!!

Part 2 -- Click Here!!