Cooling capacity for chillers is typically based on using water as the process fluid, so using a process fluid other than water could result in less cooling capacity. Heat Transport, Convection, & Dissipation. [Common Solution: reducing the temperature of the heat transfer surface often softens the deposits], Sedimentation, the depositing of dirt, sand, rust, and other small matter is also common when fresh water is used. although poorly understood. [Common Solution: reducing the temperature between the fluid and the heat transfer surface], Corrosion can destroy surface areas of the heat exchangers, creating costly damage. Typically, the energy wasted due to untreated fouling varies between 10 – 20 % of the energy required by the chillers. Applying a typical fouling factor developed for a shell and tube heat exchanger to a plate and frame design therefore will have a greater proportional effect on the U factor resulting in a greater overdesign of the exchanger. Fouling of water-cooled condensers due to scale formation, corrosion, and/or biological growth from poor water quality could also result. While in electrical chillers fouling can be compensated by an increase in energy, absorption chillers are more delicate. Plate heat exchangers can be taken apart for cleaning on both sides. Major manufacturers of air conditioning equipment generally design condensers and chiller heat exchangers to operate at a maximum “thermal resistance” or fouling factor of 0.0005. The tube side of a shell and tube heat exchanger is usually easy to clean but the shell side can be more difficult to access. How do all these variations affect the cooling capacity of a chiller? When selecting a recirculating chiller, several factors should be considered that could affect cooling capacity. Although ATCS systems are very efficient in preventing micro and macro fouling in tube &shell type heat exchangers, CQM’s SRSW Seawater disinfection systems provide an efficient solution for plate heat exchangers. As fouling increases, two things occur: First, the volume of water that can flow through the heat exchanger is reduced. What if the coolant is supplied to the process at 5°C instead of at 20°C? It seems that proper planning for the future and good design practice would result in the specification of a higher than required fouling factor for safety sake. Chiller manufacturers generally provide cooling capacity ratings based on a 20°C water delivery temperature and a 20°C ambient temperature. The manner in which fouling and fouling factors apply to plate exchangers is different from tubular heat exchangers. Later in the process, the system must raise the temperature of the refrigerant to a level above the temperature of the medium that is used for rejecting the heat. fouling rates Refrigerant Film R R Metal R M Water Film R W Refrigerant Scale (Fouling) R F Water in Tube Resistant Layers Water Heat Flow Section 9 –Heat Transfer AHRI 0.00025 fouling factor Basis of chiller ratings for condensers For evaporators 0.0001 Cu best Heat Transfer Coeff CuNi / SS options This can be controlled to a degree by the heat exchanger design. ft. F/BTU. If the chiller will be operated in a dusty or dirty environment, routine maintenance or cleaning should be scheduled and/or the chiller should be oversized. [Common Solution: reducing the temperature gradient between the fluid and the heat transfer surface.]. It is important with all heat exchangers to operate as close to the design flow conditions as possible. Fouling is the deposition and accumulation of unwanted materials such as scale, algae, biofilm, mussels, organic matter and insoluble salts on the internal surfaces of heat exchangers. For example, Aavid chillers typically operate at condensing temperatures between 32.2°C (90°F) and 43.3°C (110°F) and reject heat to 20°C (68°F) ambient air or 24°C (75°F) facility water (Figure 2). It was previously described that in the heat transfer equation the Total Thermal Resistance is the reciprocal of U clean, therefore the Total Thermal Resistance in a plate heat exchanger is often significantly less than the same application of a shell and tube heat exchanger. For instance a chiller is connected to 4 AHU.