Increasing Peak Performance

Cooling demand is typically determined by engineers based on the design conditions, which are composed of the following main factors:

• heat load caused by the outside temperature,

• heat load caused by solar radiation (this has the greatest effect through the windows),

• ventilation (to control the temperature and humidity of the supply air, the air must be cooled and heated),

• internal heat gain from people,

• internal heat gain from lighting,

• internal heat gain from electronic devices such as computers, printers, servers, heat-emitting surfaces (e.g., in manufacturing), etc.

Example of a Summer Daily Profile for an Office Building:

At night, the demand is low because typically there are no people in the building, and the outside temperature is also lower. As the outside temperature begins to rise around 7–8 a.m., people arrive and start using heat-generating electronic devices, which increases the cooling demand. The peak occurs between 12 p.m. and 2 p.m. After that, the demand decreases due to a drop in the outside temperature and fewer people remaining in the building.

Source: HeatVentors

A properly functioning cooling system must deliver exactly the required cooling capacity.

• If the cooling system produces excess capacity, the temperature will begin to decrease (in the case of comfort cooling, the air temperature; in the case of technology, the process or product temperature, etc.), which always results in additional costs and may lead to discomfort or quality degradation.

• If the cooling system produces less than the required capacity, the temperature will start to rise, which can also result in discomfort or quality degradation.

When reducing peak demand, the primary goals are to protect the cooling system and to improve efficiency. However, there may be situations where the existing system cannot meet the peak demand:

• The increased peak demand (e.g., due to changes in building usage or function, the effects of global warming, or reduced cooling capacity of an aging system) exceeds the capacity of the cooling system.

• It is not possible to install a larger cooling system because it would overload the electrical infrastructure.

The diagram below illustrates how the cooling demand of an office building is met during peak hours. The blue curve represents the cooling demand (which the system alone cannot meet without the HeatTank), the red curve shows the operation of the cooling system, and the green curve represents the operation of the chiller after the HeatTank has been integrated.

Source: HeatVentors

The chiller’s peak capacity is marked as 1 (i.e., 100%), but the current peak demand is 1.2 (i.e., 120%). This means that 20% of the cooling demand is not being met, and during peak periods, the temperature and quality of comfort are inadequate.

By timing the discharge of the HeatTank Intelligent Thermal Battery to coincide with the peak demand, the system can meet the full cooling requirement through the combined operation of the chiller and the HeatTank.