Absorption Refrigeration

[olmedo]

Can somebody tell me please why I should not use an absorption type refrigeration for room cooling as against the conventional vapor compression system.

 

[briand2]

I guess someone will disagree with this (!!), but I think you'll find that the Coefficient of Performance will be considerably less for an absorption chiller; this means you'll probably pay more in running (energy) costs to do the same cooling duty.

By the way, I do actually run a couple of absorption chillers myself (each about 800 TonR capacity), but that's only because I get "cheap" steam from a combined heat and power system.

Brian

 

[quark]

Brian!

Until and unless I have cheap steam I won't disagree.

Olmedo!

The basic advantage of absorption system was (or is?) conversion of low grade energy to low grade energy. Generally electrcity is considered as high grade energy and heat as low grade energy. Conversion from high grade energy to a low grade energy is a loss. Though COP of absorption machines are almost one third that of compression machines, the net work input will be less incase of absorption system.

Some of the disadvantages

1. On LiBr-Water system, you cannot go below 5⁰C chilled water temperature with the best attainable vacuum.

2. Crystallization of LiBr strong solution is a deadly problem at lower cooling water temperatures.

3. Periodic treatment and cleaning of LiBr is required.

4. Not a stand alone system. Even steam generator failure contributes to chiller downtime.

5. Foot print area is more for same capacity.

6. Not very flexible with load variations. (capacity control is not very good. (Liquid bypass from evaporator to absorber is a common practice. This shows the inefficiency of capacity control)

7. One point where I think Brian will agree with me is that, we should spend more time with an absorption machine when compared to relatively trouble free compression machine.

Regards,

 

[lilliput1]

Absorption chillers are normaly rated for 44°F (6.67°C). Some absorption chillers can go down to 42°F with a deration in capacity. Comparative installed prices of new 1000 ton chiller in US $ per Means 2003 Cost Data are:
$406,800 for electric centrifugal
$786,000 for gas fired absorption
$509,000 for steam absorption

 

[VSSriram]

Absorption chiller will work out economical (in most cases) only if you have waste steam or cheap steam or hot water available. By the way, hot water absoprtion chillers are also available.

You will also need to have a bigger cooling tower, since the approximate factor for heat rejection calculation would be about 1.85 as against 1.25 normally used for vapour compression machines.

If you were to use HSD as fuel for generating steam, then the additional hassles of "Explosive licences", storage of diesel, etc., etc.

 

[kiwicam]

i have worked on a few Absorpers over the years and generally have found that they are only economic in a situation where there is a considerable amount of waste energy in the form of steam or medium temperature hot water to drive the refrigeration process. Due to the low COP ( generally less than 1)they become extremely inefficient if heat has to be generated to keep the absorper running. The other disadvantage is the high capital costs involved in an installation due to the requirement for large cooling towers and condenser water flows to cope with the heat rejection and the cost of building the chiller itself as there are few manufacturers and therefore reduced competion on price.
In saying this though, i have seen major energy savings in steam turnbine to electric power plants where the waste heat from the turbines drives absorpers that chill the air entering the turbines and therefore increase the efficiency of the turbines considerably. Also, there are a lot of Absorption machines used in geothermal areas where natural reserves of high pressure steam/hot water can be utilised by large wood pulp processors and the low pressure steam left at the end of the process can be used to drive absorbers to meet all of the process cooling requirements
cheers
kiwicam

 

[lilliput1]

Never go all absorption! Some chiller must be electric. Consider absorption if you have boilers idle during summer & your electric cost is high.

 

[olmedo]

Thank guys , I appreciate your comments and they are helpful to me.