1)how we design pressurisation system in the district cooling system

2) explain about staircase pressurisaion calculation for 20 story building.:o

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Sir this is a residential HVAC board. I will out of courtesy answer this question but will answer no more.

Basically, a district cooling system (DCS) distributes thermal energy in the form of chilled water or other media from a central source to multiple buildings through a network of underground pipes for use in space and process cooling. The cooling or heat rejection is usually provided from a central cooling plant, thus eliminating the need for separate systems in individual buildings.

A DCS consists of three primary components: the central plant, the distribution network and the consumer system. The central plant may include the cooling equipment, power generation and thermal storage. The distribution or piping network is often the most expensive portion of the DCS and warrants careful design to optimize its use. The consumer system would usually comprise of air handling units and chilled water piping in the building

Pressurization uses physical smoke barriers to “keep the animal in the box” by preventing smoke from escaping the dedicated zone. Besides physical barriers, the zones' atmospheres are controlled, based on fire alarm activation. Fire alarm activation initiates AHUs — either dedicated or non-dedicated — located outside and surrounding the zone of activation. The activated air handlers will direct 100% supply air into the non-fire zones. Pressurization prevents smoke from leaving its zone of origin and entering unaffected areas, resulting in a “sandwich” effect. One drawback of pressurization is that it does not require maintaining a suitable environment for occupancy. It isn't even an objective. Pressurization's only purpose is to contain smoke at its origin.

You are probably a student so this is why I am answering these questions.

I recommend you visit a commercial engineering site for further questions. I can answer no more of your questions on this board.