HVAC Absorption Chillers vs Electric Chillers

In any HVAC system,selection of chillers involve many factors to be considered judiciously.These factors simultaneously present many advantages and disadvantages to end users.For the selection of water chillers,HVAC engineers consider all these factors keeping in view all the resources they have at their facility.

Absorption chiller vs electric chiller

Comparison of Absorption Chillers and Electric (Compression) Chillers

Following is the comparison of absorption chiller and electric chiller is presented below with aim to help you to decide the type of chillers for HVAC  system.

1. Absorption chillers have COP (coefficient of performance )of only 0.54–1.1 and it competes poorly with electric chillers (rotary compressor chillers). Electric chillers on other hand have COP from 1.0 ~ 8.0. 
2. Absorption HVAC chillers occupy approximately 50% more floor area than the equivalent  electric chillers (vapor compression chillers). 
3. Additionally due to height of absorption chillers, mechanical equipment rooms must be 6–10 ft taller than rooms housing electric chillers. Finally, because the liquid solution is  contained in long, shallow trays within an absorption chiller, the floor must be as close to absolutely level as possible.
4. In HVAC system,Absorption chiller will weight at least twice as much the equivalent electric chiller  (vapor compression chiller). 
5. Due to greater  size, absorption chillers are sometimes shipped in several sections, requiring field welding for final assembly.This is not case with counterpart electric chillers or compression chillers. 
6. Most of electric water chillers are shipped from the factory with their refrigerant charge  installed.While the refrigerant and absorbent (including additives) must be field installed in absorption HVAC chillers. 
7. When we talk about noise and vibration, absorption chillers (unless direct-fired) are quiet and essentially vibration-free as compared to compression chillers (electric drive chillers). Noise and vibrations in HVAC system annoy more than anything else . 
8. Due to the potential for crystallization of the lithium bromide in the chiller if it becomes too cool, the condenser water temperature must be kept above 75–808F.There is no problem of crystallization in electric chillers (vapor compression chillers). Forget about the crystallization and stay cooled if you have installed compression chillers . 
9. Absorption water chillers require sometimes an emergency power source if lengthy power outages are more often expected. Without power and heat input, the chiller begins to cool and the lithium bromide solution may crystallize. However, as absorption chillers consume very little electric energy so a small dedicated back-up generator can serve this purpose well. 
10. HVAC system also gives importance to the amount of heat to be rejected in condenser by water cooling or air-cooling media.The heat rejection rate from the condenser of lithium bromide chiller is 20–50% greater than for the equivalent electric chiller, requiring higher condenser water flow rates and larger cooling towers and condenser water pumps. 
11. Finally, an indirect-fired absorption water chiller will be at least 50% more expensive to purchase than the equivalent electric-drive chiller. Direct-fired absorption chillers will cost almost twice as much as an electric machine, and have the added costs associated with providing combustion air and venting (stack). 
12. Absorption water chiller or lithium bromide chiller uses natural refrigerants such water and eliminate the need of CFC or HCFC refrigerants which have high global warming potential. 
13. If you have plenty of waste heat or direct fire available ,and want to reduce your electric load ,then probably absorption chillers are the best solution.But obviously all above factors are to be considered for the selection of HVAC water chillers.

HVAC Applications of Valves

HVAC Valves are such components without which we cannot control flow in pipes .Valves are needed for every media whether it is water, gas, air or any other liquid. Valves would have been needed for solids if they could have ability to flow. Like other areas, valves find its extensive use in HVAC (heating, ventilation and air-conditioning).

With special focus on HVAC, following are the some major hvac application of valves.

• Water Chiller, the heart of HVAC system, has valves on inlet and outlet lines of chilled water and cooling water. These valves are usually gate and globe valves which are used for isolation and throttling purposes. Water chiller operates on vapor compression cycle or vapor absorption cycles which also require valves internally as a requirement of thermodynamics. For example Refrigerant expansion valve is needed inside a water chiller cycle. Chilled and cooling water headers also need valves for isolation and heating/cooling changeover.
• Similar to water chillers, HVAC hot water generator has also valves on its inlet and outlet for isolation and flow control purposes. If water chiller can also act as water heater then there is no need of hot water generator obviously.
• Chilled water pumps and cooling water pumps have also isolation and throttling valves on their inlets and outlets. When we talk about water pumps then there are also check valves at the outlet of pumps to prevent reverse flow.
• Cooling towers are another hvac equipments which require valves at inlet and outlet for flow control of cooling water. Sometimes a float valve is also in the basin of cooling tower to control the level of water in cooling streams. Valves would also be needed for make-up water lines in HVAC system and cooling towers.
• Air handling units (AHUs) also need valves at inlet and outlet to regulate chilled water as per demand of cooling in the spaces depending upon the type of HVAC control system. These air handling unit valves are also connected to some HVAC software to remotely operate them as per cooling/heating demand from HVAC users. Drain valves are also provisioned inside air handling units.
• If Fan Coil Units (FCUs) are installed in individual rooms then valves will also be installed at entry and exit of these units to have precise control of cooling /heating for occupants of that space.

Tips for HVAC System Engineers

As HVAC system engineer, one has to keep an eye on all factors and areas that can decrease the efficiency of system or increase downtime or HVAC system unavailability or increase the maintenance cost of heating, ventilation and air-conditioning system. The responsibility starts from very beginning, when you decide to install HVAC system and start working on it in any way.

Following are the tips for smooth, trouble free and economical operation/working of hvac system.

1. Start your working from the very early stages of hvac system selection, procurement and tendering. Don’t ignore all these pre-installation steps as it would become difficult at later stages to alter any pre-done work. Complete your home work in selection of type of chillers you are going to install for your building or space or for other purposes. Consult hvac experts for getting pros and cons of different types of chillers and select the one which suits your resources and priorities. Then select the renowned and reliable manufacturer for purchasing the hvac system components. Get involved in tenders to ensure transparency in whole process.
2. HVAC Installation is very important phase for hvac engineers. Include all essential items and accessories in hvac contract BOQ and monitor the activities of hvac contactor so that all goes in accordance with boq or terms and conditions written while awarding contract. Ensure that all installation is carried out in accordance with drawings and all components meet the specifications mentioned in BOQ. Your saving at any stage could lead you to spend more in later stages. Never compromise the material of all items being installed in hvac system. Low quality material would finally take you to problems in coming days/years. Commissioning is as important as its installation so adhere to commissioning procedures at all times and don’t ignore any thing in courtesy.
3. Training of hvac personnel is very important in operation and maintenance point of view. So include training of your personnel in contract or arrange it separately. Your expenditure on manpower training would pay back you in future so never overlook it.
4. Prepare all hvac procedures related to operation and maintenance of each and every component of hvac system and implement it strictly. Adhere to maintenance program for your water chillers, air handling units, cooling towers and fan coil units .Your adherence to maintenance programs would never let you face any problem regarding the unavailability of hvac system. Always try to complete maintenance work timely in the best available resources or with the support of hvac supplier
5. Adopt hvac pro-active approach regarding critical and heat transfer interfaces/surfaces or to operate hvac system at maximum efficiency, focus on heat transfer interfaces/surfaces. In this regard condenser is most important, keep it at optimum conditions. Scaling, corrosion and high pressure in condenser would get you in trouble finally so be pro-active before your condenser lets you down. Heating and cooling coils are also equally important as these would directly affect cooling or heating in hvac spaces/zones. Get all coils cleaned and keep them in best heat transfer condition. Ensure timely maintenance of cooling towers to operate them at maximum efficiency/effectiveness.

Water Cooled Chiller vs Air Cooled Chiller in HVAC System

• Initial cost of air cooled chillers is lower than water cooled chillers as air cooled systems don’t require cooling towers,condenser water pumps and associated HVAC components.
• Small systems are almost always air-cooled since the extra requirements of water treatment and maintenance are capital intensive and will not be offset quickly by the lower operating costs.  Larger HVAC water chillers are almost always water cooled .HVAC engineers and technicians feel easy with maintenance free or less maintenance equipment.
• Water cooled chillers may be preferred because of  better heat transfer properties of water as compared to air cooled chillers.The primary advantage of water is that the film coefficient is 10-100 times better with water than air.Film coefficient controls heat transfer with given constant area and temperature difference.
• Water-cooled HVAC units make less noise and give more cooling per square foot.While air cooled chillers have comparatively less cooling per square foot and are more noisy HVAC machines.Noisy machines are annoying especially for occupants of nearest offices or zones.
• While comparing  air and water cooled chillers, an overall system cost (both running and installed) has to be worked out. Size of HVAC unit matters when selecting the water cooled chiller or air cooled chiller.Smaller HVAC units are usually air cooled, larger are water cooled.
• HVAC engineers have to evaluate air cooled and water cooled chillers keeping in mind various factors.Refrigeration engineer has to consider the ambient conditions (wet bulb and dry bulb), number of hours of operation, part load pattern and cost of maintenance etc.
• HVAC experts have no single answer to when asked “water cooled chiller is better or air cooled chiller?”. The fact is that “It all depends”. Water-cooled chillers will normally condense at an average lower pressure than air-cooled chillers.  This is because the water temperature will usually be less than the air temperature.If your condenser is operating at lower pressure then it is directly reflected and translated into lower operating costs or KW /TR(Ton of refrigeration).
• The difference between the wet-bulb temperature and the dry-bulb temperature gives the available difference between the condensing temperatures of water-cooled and air-cooled condensers respectively.  
• Cooling towers and/or evaporative condensers have main disadvantage of maintenance and water treatment costs. This running cost is not present in air cooled chillers.
• Despite the advantages of lower IKW/TR of a water-cooled system or water cooled chillers, sometimes, air-cooled systems are preferred for various applications.
• For example in 24 hour application of HVAC chillers,the night time dry bulb temperature are generally much lower than the day time dry bulb temperature, as compared to the difference in wet bulb temperature between day and night.  This advantage is best capitalized by an air-cooled system or air cooled chillers.
• Other examples could be where the wet bulb temperatures are very high, especially coastal areas. 
• When comparing water cooled and air cooled chiller,scarcity of water and hence cost of water is another issue which is a point to be considered while deciding on the system.  This happens in many countries .
• Space is also of importance in some applications. Air cooled chillers can utilize open space, such as a parking lot, roof or ground level area. Although smaller in size but Water cooled chillers require a mechanical room and cooling towers.
• Air recirculation is very important for air cooled chillers.Any obstruction in the circulation of air near water chillers would adversely affect the performance of air cooled chillers.Air cooled chillers can have problems with recirculation if there are walls higher than the unit or too many units to close together. If there is a situation where outside walls are required for building code and the unit will not be receiving enough fresh air, then a water cooled application may be the best option.
• Water cooled chillers have longer life,higher efficiency,large capacity and also refrigerant containment.While looking on disadvantatges of air cooled chillers,they have lower efficiency,comparatively short life span and available in low capacity range.

5 Heat Transfer Loops in HVAC System

Several heat transfer loops work in an HVAC system .In these heat transfer loops heat energy is exchanged to achieve the ultimate purpose of heating and cooling of air in HVAC system. 

These heat transfer loops are basic organs of any HVAC system. Problem in any of these loops affects the HVAC system .In these heat transfer loops thermal or heat energy moves from left to right as it is extracted from the space and rejected into surroundings or air through five loops of heat transfer.

Heat transfer loops in HVAC system

1. Indoor air loop in HVAC system  

In the left loop, indoor air is driven by the supply air fan through a cooling coil, where it transfers its heat to chilled water. The cool air then cools the building space or different HVAC zones.

2. Chilled water loop in HVAC system

Driven by the chilled water pump, water returns from the cooling coil to the chiller’s evaporator to be re-cooled.

3. Refrigerant loop in HVAC system

Using a phase-change refrigerant, the chiller’s compressor pumps heat from the chilled water to the condenser water.

4. Condenser water loop in HVAC system

Cooling water absorbs heat from the chiller’s condenser, and the condenser water pump sends it to the cooling tower.

5. Cooling tower loop in HVAC system

The cooling tower’s fan drives air across an open flow of the hot condenser water, transferring the heat to the air.Thus cooling tower rejects heat to atmosphere in this way.

HVAC System

HVAC system is basically an assembly of various types of equipments installed together to provide heating and cooling alongwith indoor climate control. HVAC systems involve mechanical, electrical and I & C components to provide comfort to the occupants of building/space or to preserve goods,products or items placed in space.

HVAC System,HVAC water chillers

HVAC cooling systems may be integrated with HVAC heating systems or these may be installed separately depending upon HVAC design  .HVAC system also serves on industrial scale to keep the machinery running by maintaining the temperature of space/hall/room where machines are installed.HVAC water chillers have become essential for any industry for its various needs.

HVAC System Basic Components

An HVAC System may include the following basic components or units.

• HVAC water chillers and heaters
• Hot water generator (if chiller does produce chilled water only) or furnace
• Chilled water pumps
• Cooling water pumps
• Electrical power supply control or Motor control center (MCC)
• Cooling towers
• Piping for chilled water and cooling water or condenser side water
• Valves for chilled water and cooling water sides
• Air handling units (AHUs) , heating coils and cooling Coils
• Ducts in ventilation system (supply ducts and return ducts)
• Fan Coil Units (FCUs) and thermostats
• HVAC Diffusers and grills
• HVAC controls (instrumentation & Control components)  installed at various locations
• HVAC software for building HVAC control or building management system (BMS)

An Assembly of all above components forms an HVAC system.

HVAC system working principle is explained as below.

In the background of HVAC system ,an HVAC water chiller produces chilled water which is then circulated throughout the building or space upto cooling coils in air handling units.Blowers move air on cooling coils which is then distributed into various portions of space or building for providing comfort or preserving goods/items as per HVAC design.Air is distributed through supply ducts and return air is collected in air handling units with the help of return ducts.Chilled water and cooling water pumps provide energy to keep the chilled and cooling water moving.

HVAC Valves are also installed at various points in piping to ease the maintenance of HVAC system or for the sake of system control.Heating of air may be done with the help of HVAC heat pump ,hot water generator or simply by furnace.Some industrial chillers also serve as heaters in winter season.Heating coils take the place of cooling coils in case of heating mode.

HVAC system cost may vary for different applications as heating and cooling space or environment  varies. Looking for cheap hvac systems may involve little research in types of HVAC systems and HVAC suppliers otherwise you would be lamenting over waste of millions of dollars for selecting wrong HVAC designer & contractor.

What is an HVAC ?

Acronym HVAC stands for heating ,ventilation and air conditioning. Sometimes Refrigeration "R " is also added and it becomes "HVACR".HVAC is basically climate control of confined space with respect to requirements of persons or goods in it.HVAC system is not only heating and cooling of air but also concerned with mainatining the indoor air quality (IAQ).Heating of air is done usually in winter and similarly cooling of air is done in summer season.

HVAC

HVAC system works on the principles of thermodynamics ,fluid mechanics and heat transfer.


All these fields come into play in various components of HVAC.IAQ Indoor air quality is the quality of air inside the building or structures as mostly related to health and safe keeping of its occupants or items/goods placed.IAQ is changed with inclusiion or contamination with gases  and uncontrolled mass & energy transfer.


HVAC systems are used for heating and cooling  & air condition in homes, building, industry, vehicles, aquariums and many more.With the passage of time application of HVAC are increasing and more research is in-progress in this field.HVAC business is also increasing at the same pace as field of application is broadening.