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DYNAMICS OF PRIMARY/SECONDARY CHILLED WATER SYSTEMS...

By Kirby P. Nelson, P.E. Paul Mueller Company Springfield, Missouri...

he purpose of this paper is to bring some additional understanding to the dynamics of variable flow chilled water systems. The literature has had several articles in recent months on this subject with some disagreement regarding a check valve in the bypass line. Reference (1) gave an example of a very positive result after the installation of a check valve. This paper will show a similar result and try to illustrate the reasons for the improvement. The Reference (1) article also presents information on load degradation as a chilled water system ages and, therefore, requires colder supply water and greater flow. This paper will present a study of the dynamics of a new and aged primary/secondary system based on a computer simulation which includes the characteristics of a specific chiller and the laws of thermodynamics. We will analyze the effects of restricting flow in the bypass line and also look at the dynamics of adding thermal storage to the system....

BALANCED SYSTEM...

We define the balanced system to be essentially zero flow in the bypass line at peak cooling load. We will assume the load is designed for a delta temperature of 16 F and a peak design load of 15,150 tons. The primary pumps provide constant flow through the chiller with variable flow to the load. Our selected chiller is a 2,165-ton unit at peak conditions. Therefore, seven chillers will meet the peak load. Figure 1 illustrates the temperatures and flows at this near-balanced condition. Note that there is a small negative flow in the bypass line of 305 gpm due to the difficulty of exactly matching a chiller system to the load. Table 1, Column 1 shows the same data for this balanced condition. (See References 2 and 3 for additional discussion.) The chiller is modeled as providing about 2,165 tons for a chiller entering temperature of 60 F and 1,700 tons for an inlet temperature of about 48.5 F....

Figure 1 - Balanced System...

Nomenclature...

Load in Tons Delta T Tls Fls Tlr Fb Tb = Tls - Tlr ( F) = Temperature load supply ( F) = Flowload supply (gpm) = Temperature load return ( F) = Flow in bypass (gpm) = Temperature of bypass flow ( F) Fce Tce Tcl Tpl = Required flow entering chillers (gpm) = Temperature entering chillers ( F) = Temperature leaving chillers ( F) = Temperature after bypass ( F)...

Chillers On = Number Running % Load Assumes Chillers Share Load Eq...

Document Keywords

Dynamics of Primary/Secondary Chilled Water Systems product divisions ice systems group pdfs dcws

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About Paul Mueller Company

Paul Mueller Company, centrally located in Springfield, Missouri, specializes in the design and manufacture of stainless steel tanks and processing systems and equipment for the food, dairy, beverage,...

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