Q3 You are the professional engineer appointed to design an air-conditioning sys
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Question
Q3 You are the professional engineer appointed to design an air-conditioning system for "Sun-rise Cafe", which has an internal volume of 400 m, according to the following requirements: Required Room Room Loads for Outdoor Air Air Interchange Latentfor Design Purpose Satisfy Fresh Air RH(%) 1 Requirement (N) Conditions Air-conditioning Conditions Adoptedper Hour to Sensible OC DB RH ( kW 24 60 9.2 30 75 4 An adiabatic mixing chamber, a cooling coil, a re-heater and a fan (with negligible heat gain) are arranged to form the air-conditioning system. Temperature increased by the supplied air after circulating through the room is 8 °C. Re-circulating air should be used as long as the fresh air requirement is fulfilled. Perform the following tasks related to the proposed air-conditioning system with the aid of the provided equations and psychrometric chart: Specify all air-conditioning processes on the provided psychrometric chart; Determine the heat removal rate and the condensation rate at the cooling coil; and Determine the heat addition rate at the re-heater (a) (b) (c) he used psychrometric chart should also be submitte ual meanings Room Sensible Load: s-CAr Room Latent Load: (a-m (??) (dW Mass Flow Rate of Ambient Air for Fresh Air Requirement: - Latent heat of H20 at low pressure 2550 kJ/kg Specific heat (CP) of dry air- 1.005 kJ/kg KExplanation / Answer
An air conditioner (AC) in a room or a car works by collecting hot air from a given space, processing it within itself with the help of a refrigerant and a bunch of coils and then releasing cool air into the same space where the hot air had originally been collected. This is essentially how air conditioners work.
Imagine that you’re outside in the sweltering heat of a particularly hot summer day, running some godforsaken errands that couldn’t be put off any longer. The heat is so unbearable that it feels like the hottest day on Earth since the dawn of civilization. However, there is one thing that keeps you going: the knowledge that you’ll be inside your air conditioned home in one hour.
Finally, that moment comes. You open the door and step inside your house. A gust of chilled air envelops every cell of your body and you instantly feel better.
Central air conditioner unit is an energy moving or converted machines that are designed to cool or heat the entire house. It does not create heat or cool. It just removes heat from one area, where it is undesirable, to an area where it is less significant.
Central air conditions has a centralize duct system. The duct system (air distribution system) has an air handler, air supply system, air return duct and the grilles and register that circulates warm air from a furnace or cooled air from central air conditioning units to our room. It returns that air back to the system and starts again.
It uses Ac refrigerant (we may know it as Freon) as a substance to absorb the heat from indoor evaporator coils and rejects that heat to outdoor condenser coils or vice verse.
Central air conditioner units used a blown, which is mounted indoor to a furnace to circular that cold air to the entire house through air distribution system (duct). It uses the same duct system for heating and cooling.
How does air conditioning work?
Home ac works by removing heat from one location and rejected to different location.
Central air conditioner units using the compressor, the condenser fans, the blower and the air conditioner unit’s electrical parts to make the ac units work. Central ac units work by using an electrical energy and converted it to mechanical energy.
To have an idea of how central air conditioning unit works. We have to understand the basic five mechanical components and how the basic refrigeration cycle work.
As a result of condensing the hot vapor heat, the refrigerant turns to liquid.
Once the refrigerant’s tube connects to these components, and we add refrigerant in it; It is now known as refrigeration cycle (close- loop air conditioner units).
The copper tube comes in many differences sizes, purpose and some of it comes with an insulator.
The operation principle:
Central air conditioner unit is simply a matter of removing heat from indoor (evaporator coil) to outdoor (condenser unit) by using the four basic mechanical components:
The compressor, the condenser, the expansion device, the evaporator and the refrigerant copper tube that connects these components.
If we understand how the basic refrigeration cycle works, we understand how any air conditioner units work. Since all air conditioner units have the same basic components, refrigeration cycle and air conditioning theory.
It doesn’t matter if it’s window ac, packed air conditioner, ductless air conditioner, portable air conditioners or central air conditioning units..
Basic residential air conditioner terms
This shows us the total heating output (supply heat) in Btu (including electric heat) during heating season and compared to the total electricity energy heat pump consumed (in watt/hr) in the same season and we get HSPF.
Central air conditioner ratings
Residential air conditioner is rated in Seasonal Energy Efficiency Ratio (SEER) – It is the measurement of central air conditioning unit or heat pump efficiency rate in Btu over cooling season.
It’s the total cooling output (supply air) of an air conditioning Btu we get out during its normal usage periods (approximately 4 months) and then divided to electricity energy the central air conditioners consumed (watt/hr) in that same cooling season and we get SEER.
Why do we size central air conditioners and how?
The reason HVAC contractor does this is to find the correct size air conditioner units (measure in ton) we'll need for a replacement central air units or for a new house.
Some HVAC contractor size air conditioners by the rules of thumb (guesstimate) over the phone, which is fine. Not every contractor has the luxury to attend every home to provide estimation, but the finish sizing should be done properly on paper.
If an HVAC contractor does not have a properly load calculation we either have an oversized or undersized equipment.
Types of central air conditioner units
There are two types of central air conditioner units we will see:
a split system air conditioning and package air conditioner units.
Split system air conditioning
Split - system have the two separate metal cabinets for indoor and outdoor. These two cabinets are connected to each to other with copper refrigerant tube.
Indoor units, which are also known as air handler. It contains the blower, furnace (for heat season), metering device, evaporator coils, control, and other electrical parts.
The condenser is located outdoor, it has a square or round shaped metal cabinets containing a compressor, condenser fans, and condenser coil plus the electrical parts.
In a split-central air conditioner unit or any air conditioner units the major components must be compatible. Each major component must have the same capacity rate, if an indoor unit is 13 SEER the outside units also have to be 13 SEER.
Make sure to have manufacture equipment specification sheets, it tells us the component’s capacity and what the equipment is designed for. If we do not know the information, find out the brand name and called the manufacture.
Package air conditioner units
Package unit is a self-contained air conditioner units, which have all the components built into one metal cabinet. Package air conditioners are normally located beside the building, on top of roof or on a window.
Window air conditioning is a package air conditioner, except its small, has less capacity, and it has the one fan motor with a double shaft that runs the blower and condenser fan. While larger package air conditioner units have a 200 ton of air conditioning or heating capacity with two motors fan. One fan is for evaporator and the other for condenser.
A rooftop unit in light commercial is normally air-to-air or air cooled air conditioner units. It’s on top of the building just to save building space.
Even though package air conditioner unit is located outside or on top of the roof, it needs an air distribution system, control connection and must be connected to a power line by a licensed electrician. Except window units, it does not need a duct system it just blows air freely to open space.
There are different types or arrangement of package air conditioner systems.
Air-to-air package unit or air cooled package unit is similar to window air conditioner except it has an air distribution system and two motor fans.
The term air-to-air means that it uses air as the condensing medium, it absorbs heat from the inside air and rejects it into outside air or vice versa. Air-to-air package system is the most common system used in residential and light commercial.
Air-to-water sometimes known as water cooled package unit, absorbs the heat out of conditioned space air and rejects that heat into water. This water could be waste, reused, or go through a cooling tower to reject the heat to surrounding (ambient) air.
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