OMNICO Engineering - Industrial Refrigeration and HVAC - Your Partner in Green Solutions

OMNICO Engineering - Industrial Refrigeration and HVAC - Your Partner in Green Solutions
HVAC and District Cooling Systems

HVAC and District Cooling Systems (DCS)

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Pressure Vessels ASME

HVAC - Heating, Ventilation and Air Conditioning
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With advances in technologies to deal with design and safety issues, and the increasing emphasis on using refrigerants that do not deplete the ozone layer or contribute to global warming, ammonia is experiencing a renaissance. It is gradually gaining acceptance across a wide range of air-conditioning installations where specifiers are seeking the optimum in energy-efficient cooling systems that also have a minimum impact on the environment. This even includes installations in public areas such as offices, hotels, supermarkets, hospitals and airport terminals where, previously, the toxicity and flammability would have precluded the use of ammonia.
District Cooling Systems
NS TWINPAC screw chiller at Heathrow Airport

"Future Proof" Refrigerant
Property investors are typically calculating with medium to long term depreciation on chillers in the financial projections. For buildings using chillers with HCFC and HFC refrigerants, owners are faced with a number of uncertainties which pose serious future threats to the investment and the company as a whole; Owners need to ask themselves the following basic questions:

  • - Is the refrigerant going to be available in the future in our country/market?
  • - How much will the price on refrigerant increase in the future?
  • - How will we as a company or Governmental institution be perceived by others in the future if not contributing to the cause against climate change to the degree which is expected of us?

Screw PAC - Principle
Screw PAC - Principle

Facts are, Governments and the international community are committed to phasing out refrigerants that are harmful to the environment. Ammonia has zero ozone layer depletion or global warming potential, it is cheap and is guaranteed available for the entire chiller lifetime.

With all this going for it, why has ammonia not been used more extensively for air-conditioning applications until now?

The main reasons are its potential flammability and its toxicity, which necessitate certain safety precautions, and its aggressive chemical reaction when in contact with copper. Early ammonia designers also faced difficulties with refrigerant-flow control and oil return. These disadvantages were behind its fall from grace in the 1950s when the, apparently, safer CFCs became popular.

So long as health and safety guidelines are adhered to, there is no reason why ammonia should not be used in any application. Responsible manufacturers include safety features as standard and are increasingly introducing models with innovative engineering to allow an exceptionally low refrigerant charge, which reduces the risks associated with a possible leak.

In a plant room, the usual method of installation is to build an enclosure around the chiller to include an ammonia detection alarm system, normal ventilation fan and motorized damper. Nearby would be an ammonia 'scrubber', bearing in mind that ammonia is highly soluble in water.

Under normal conditions, air will be circulated around the plant room. If a leak is detected, the ventilation fan is switched off, the damper shut and the scrubber started. This draws the air out of the enclosure and effectively 'washes' it with water to absorb the ammonia. As a result, there is no danger of ammonia being vented either inside or outside the building, and there is no exposure risk for anyone entering the plant room. In the unlikely event of this happening, the waste water, with a very low concentration of ammonia, can usually be allowed to pass straight into the normal building drainage system.

M&M Chiller Packages
M&M Chiller Packages

Low Operating Cost - Excellent Part Load Performance

Most chillers only rarely operate at maximum capacity. A predetermined chiller operating scenario has been established by the world's leading chiller manufacturers (ARI Standard 550/590) to compare the anticipated chiller operating costs of different designs and refrigerants based on realistic operating conditions;

  • - 100% capacity: 1% of the time
  • - 75% capacity: 42% of the time
  • - 50% capacity: 45% of the time
  • - 25% capacity: 12% of the time

PAC chillers with flooded evaporator and water cooled condenser of plate-heat-exchanger type have excellent part load characteristics as approach temperatures get increasingly closer when chiller capacity decreases. This is limited by decreasing part load efficiencies of motor and compressor however, can be mitigated by using variable speed drive and motor, which in most cases are paid back in a matter of months.

Due to the PAC chillers' durable and heavy duty design, and the plate material of plate heat exchangers, which are available in various grades of stainless steel (AISI316 is standard) or Titanium, the investment cost is usually higher than that of conventional centrifugal or screw chillers. However, the premium investment usually pays off rapidly - Typical pay-back time is in the 1 to 3 year range subject to actually running conditions, cost of electricity and tariffs.
PAC chillers - The future-proof investment and the obvious choice for responsible investors aiming at sustainable income and high quality earnings.

There is no doubt that ammonia has now been firmly re-born into air conditioning. Its future-proof potential and environmental advantages will ensure this is not just a passing vogue but represents a long term, viable alternative to HCFCs and, even, HFCs.

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