Issue 5, Volume 7, 2013 197 Design optimal of refrigeration insulations Ioan Sarbu, Emilian Stefan Valea, and Gabriel Ostafe transfer equation which admits a heat gain so that neither Abstract—Economic operation with minimal energy con- results too thick expensive insulation, nor very high cool sumption and low costs of a cooled room or a refrigerant piping consumption. In specialty literature [2], [11] are recom- system depends largely on the quality and thickness of their mended thicknesses for refrigeration insulation based on insulation. The classical method of insulation rating for refrigeration condensation control or for limiting heat gain. systems is based on respect of the condition to prevent condensation The most economical insulation thickness can be of water vapours in the air on the surface of insulation or on limiting heat gain, but rarely leads to optimum in terms of a technical and determined by considering both initial costs and long-term economic criterion. In this paper are described some types of energy savings. Optimal computation of the insulations applied insulation for refrigeration applications and is developed a rating to cooled rooms and to cold pipes based on economic criteria optimization model of these insulations with a high level of of minimum total life-cycle cost leads to insulation thickness generality. It uses multiple dynamic optimization criteria simple or that applied in practice become incorrect at some point after compound, which better reflects the economic and energy complex the execution, because price evolution in time. The energy aspects, present and future. Based on this model were elaborated two costs are volatile, and a fuel cost inflation factor may increase computer programs implemented on PC microsystems. Numerical more quickly than general inflation. examples will be presented to demonstrate the accuracy and In this paper is developed a computational model of the efficiency of the proposed optimization model. These show the good performance of the new model. optimal thickness of these insulations, with a high level of generality. This model uses multiple dynamic optimization Keywords— Cooled rooms, Refrigerant piping, Insulation rating, criteria simple or compound, which better reflects the Optimization model, Comparative analysis. economic and energy complex aspects, present and future. Based on this optimization model are elaborated two computer I. INTRODUCTION programs implemented on PC microsystems. HE role of refrigeration system insulation is to reduce heat II. TYPES OF INSULATION FOR REFRIGERATION APPLICATIONS Tflow to cooled spaces or to cold devices and pipes in which the refrigerant temperature below ambient temperature Refrigeration systems cover a broad spectrum of application (free air, soil or neighbouring rooms). Therefore, refrigeration temperatures and environments. But they all face the same insulation is commonly used to reduce energy consumption of issues relating to both condensation control and moisture. Since moisture is a good thermal conductor, its presence in an refrigerating systems and equipment. insulation system is highly detrimental. Unlike hot systems, Economic operation of a cooled room or a cold pipe where marginal insulation may result in increased energy use depends largely on the quality and thickness of their insulation. (and added cost), refrigeration systems face condensation, Hence the proper selection importance of the insu-lation which often leads to complete system failure. Even with material and rating of their refrigeration insulations, leading to today’s high energy costs, the design thickness in most judicious use of investment funds, to normal operation with refrigeration applications is dictated by what is needed to minimal energy consumption and low costs. prevent condensation, rather than by economic payback. Cellular glass, flexible elastomeric, mineral wool, polyiso- Refrigeration systems typically operate in the range of −5°C cyanurate, and expanded or extruded polystyrene are insu- − lation materials commonly used in refrigerant applications. (for Freon systems) to as low as 45 °C (for ammonia The classical method of insulation rating for refrigeration systems). They can use a variety of refrigerants and fluids in systems is based on respect of the condition to prevent addition to Freon and ammonia, including glycol, brine, and condensation of water vapours in the air on the surface of other specialty fluids. Copper, iron, stainless steel, or other insulation, but rarely leads to optimum in terms of a technical piping materials may be used to carry the cooling medium. and economic reason. In case of flat surfaces is used heat Typical applications include those in supermarkets, beverage−dispensing lines, chillers, and food processing, freezing, and storage facilities. Other applications include Ioan Sarbu is currently a Professor and Department Head at the Building Services Engineering Department, “Politehnica” University of Timisoara, those at ice rinks and various unique applications. All of these 300006 ROMANIA, e-mail address: [email protected] applications share common concerns regarding condensation Emilian Stefan Valea is currently a Lecturer at the Building Services control and long-term reliability, but they also have particular Engineering Department, “Politehnica” University of Timisoara, 300006 issues with installation, required thickness, and the ROMANIA, e-mail address: [email protected] Gabriel Ostafe is currently a Assistant Professor at the Building Services environmental conditions in which they operate. Engineering Department, “Politehnica” University of Timisoara, 300006 ROMANIA, e-mail address: [email protected] INTERNATIONAL JOURNAL of ENERGY and ENVIRONMENT Issue 5, Volume 7, 2013 198 Reliability should be the primary concern when considering The insulation system installed on a supermarket the design and installation for any application. Design must refrigeration system must be highly reliable, as it will operate consider factors including the application temperature, 24 hours a day for up to 10 years. Closed-cell elastomeric environmental considerations, consequences if a failure occurs, materials have been used in this application for many years and expectations of the job by the owners (longevity of the because they are extremely reliable and cost-effective. It is a system, aesthetics, etc.). The following are some important primary product used for supermarket refrigeration features of the insulation in various refrigeration applications: applications because of its low WVT, allowable use − thermal conductivity; temperature range, and ease of installation. − water vapor transmission (WVT) properties; Using a coating or flexible jacketing can improve the − water absorption properties; appearance, durability, weather resistance, and longevity of the − coefficient of thermal expansion; insulation on a unit. Flexible, closed-cell elastomeric − moisture wicking. insulation is the predominate product used in this application. There are recommended the following insulation materials A 2.0 cm thickness is commonly used. for refrigeration applications [2]: cellular glass, closed-cell Food processing, freezing, storage, and distribution phenolic, flexible elastomeric, polyisocyurante, and applications often use ammonia refrigeration because of its polystyrene. All of these materials are closed-cell foam lower operating costs. materials, which means they will have good WVT and low As ammonia systems are designed for smaller applications water absorption characteristics. at an economical up-front cost, they are getting more In all cases, the entire system (seams, butt joints, and consideration than more expensive operating systems. While termination points) must be completely sealed with adhesives most areas do not exceed high temperatures above 70 °C, to protect against air intrusion into the system, which would some sections may cycle from −40 °C to 120 °C. Lower carry moisture and result in condensation between the cold temperatures (down to −20 °C) mean greater insulation pipe and the insulation. Relying on a single, concentrated thickness (5−8 cm) is usually required to prevent vapor retarder is not recommended. Generally, closed-cell condensation. Typically, 8 cm of insulation is used to prevent foam insulations are used for these applications. Seams should condensation, as many of these applications are in high- be minimized. On multilayer systems, the seams should be humidity areas. The majority of the insulation is installed staggered. Taped seams are only allowed as a complimentary outdoors, so jacketing selection is critical. As a result of the closure system. cost and thickness required, polystyrene and polyisocyurante Supermarkets are one of the biggest and most noticeable with a stainless steel jacket are the most common materials applications for refrigeration systems. They face several used. Of key concern is corrosion of iron pipe. Proper issues, including changes in refrigerant, colder line insulation installation (with no open or through seams) is a temperatures, higher temperature hot gas defrost cycles, major concern, and use of secondary vapor-retarder systems is changing store designs, and pressures to reduce installation the norm. time to decrease store build time. In [2] are detailed many of The refrigeration market covers a broad spectrum of the issues related to this market segment. applications, each with unique requirements but all with a Using preinsulated