MAKKAH, Saudi Arabia, 19 April 2021: With the pandemic still posing a threat to the lives of many, the Government of Saudi Arabia has set strategic plans to implement all necessary precautionary measures at the Two Holy Mosques for this year’s Ramadan, to ensure the health and safety of pilgrims. Al Salem Johnson Controls (YORK) said that the YORK-driven HVAC system at the Two Holy Mosques is a vital part of the precautionary measures, to control temperatures and humidity and the purity and freshness of cold air inside them, for infection control and to prevent its spread.

The two cooling plants for the Holy Mosque in Makkah (Shamiya and Ajyad) and the Prophet’s Mosque in Madinah (the Central Cooling Plant) are among the largest plants in the world, Al Salem Johnson Control said. The YORK system in the Two Holy Mosques, the company said, is divided into two parts: YORK chillers inside the cooling plants, and the Saudi-made YORK air- handling units (AHUs), which distribute cool and fresh air inside the Mosques.

In light of the ongoing pandemic, the importance of AHUs is more profound than at any other time, as they ensure the quality, freshness and purity of the indoor air, through a highly efficient filtration technology, which limits the spread of diseases and airborne viruses, and prevents dust particles from passing through the air ducts, the company said. Its AHUs, it added, guarantee the comfort of pilgrims and worshipers as well as protect the structure of the Two Holy Mosques, by controlling temperature and humidity levels and by balancing the airflow.

The YORK chillers cool the water, then pump it to the AHUs, where a heat exchange occurs between the warm air entering the unit and the chilled water inside the tubes. As the cold fresh air flows to all parts of the Two Holy Mosques, the water that absorbed the entering air temperature, returns to the cooling plant to be re-cooled inside the chillers, and re-pumped to the Mosques, the company said.

The chilled water flows in a closed circuit, thus directly not touching the air. Therefore, on the one hand, the air is not affected by the refrigerant, and on the other hand, no airborne microbes or bacteria enter this water. As a result, when the chillers reject the heat absorbed from the air of the Mosques outside the district cooling plants into the atmosphere, accompanied by small amounts of water vapour, it is free of any biological or chemical pollutants, preserving the safety of the environment and the health of individuals in the areas surrounding the cooling plants, the company said.

In a continuous cycle, the air moves around the Two Holy Mosques, absorbing heat from the atmosphere and from the pilgrims’ bodies, catching dust particles and some airborne bacteria or microbes on its way to the AHUs. Inside the AHUs, this air first passes through several high-efficiency filtration stages, to trap the dust and microbes, then flows over the cooling coils containing the chilled water. The filtered, fresh, cooled and dehumidified air then blows out of the AHUs into the Mosques to repeat its cycle again.

The AHUs control the fresh air flow rates through several technologies, including partial closure of the air outlets, or by means of a Variable Speed Drive connected to the fans for speed control, thus ensuring flow rates, as needed, the company said. Energy efficiency, the company said, is achieved through controlling the fresh air flow from the AHUs, on the one hand, and controlling the cooling capacity and energy loads of the chillers, on the other hand, based on the congestion inside the Two Holy Mosques. For chillers, the difference in temperatures of the chilled water flowing back and forth between the chillers and the AHUs indicates the momentary congestion inside the Mosques, the company said. Thus, both the cooling capacity and power loads are reduced when the number of people is limited, while are raised at peak times, such as prayer times, the company said.

The entire HVAC system, the company said, has been designed keeping in mind the crowded nature of both places throughout the year, especially during the peak seasons of Ramadan and Haj.