Chiller Plant Design . The system consists of a chiller, cooling tower, building cooling load, chilled water and condensing water pumps and piping. This section will review each of the components. Figure 1 - Single Chiller Loop. Chiller Basics. The chiller can be water- cooled, air- cooled or evaporatively cooled. Ontario Building Code 2012 2013 WWW.ORDERLIN E COM The compressor types typically are reciprocating, scroll, screw or centrifugal. The evaporator can be remote from the condensing section on air- cooled units. This has the advantage of allowing the chilled water loop to remain inside the building envelope when using an outdoor chiller. In applications where freezing conditions can be expected, keeping the chilled water loop inside the building avoids the need for some form of antifreeze. There can be multiple chillers in a chilled water plant. The details of various multiple chiller plant designs will be discussed in future sections. ![]() CSA Group is an independent, not-for-profit member-based association dedicated to advancing safety, sustainability and social good. We are an internationally. MODEL 4200-IR Refrigerant Monitor with Infrared Sensor Transmitter User Manual Technical Support Continental North America Toll Free 1-(800) 387-9487. SOMMAIRE DE DIRECTION. CanmetÉNERGIE à Varennes a réalisé cette étude pour répondre aux interrogations des propriétaires d’arénas et de plusieurs organismes. Engineering Data Section One Design Goals . The chilled water flows through the evaporator of the chiller. The evaporator is a heat exchanger where the chilled water gives up its sensible heat (the water temperature drops) and transfers the heat to the refrigerant as latent energy (the refrigerant evaporates or boils). Flow and Capacity Calculations. For air conditioning applications, the common design conditions are 4. F supply water temperature and 2. The temperature change in the fluid for either the condenser or the evaporator can be described using the following formula: Q = W . The water temperature entering the evaporator is then 5. F. Most air conditioning design conditions are based on 7. F and 5. 0% relative humidity (RH) in the occupied space. The dewpoint for air at this condition is 5. F. Most HVAC designs are based on cooling the air to this dewpoint to maintain the proper RH in the space. Using a 1. 0o. F approach at the cooling coil means the supply chilled water needs to be around 4. F or 4. 5o. F. The designer is not tied to these typical design conditions. In fact, more energy efficient solutions can be found by modifying the design conditions, as the project requires. Changing the chilled water flow rate affects a specific chiller's performance. Too low a flow rate lowers the chiller efficiency and ultimately leads to laminar flow. The minimum flow rate is typically around 3 fps (feet per second). Too high a flow rate leads to vibration, noise and tube erosion. The maximum flow rate is typically around 1. The chilled water flow rate should be maintained between these limits of 3 to 1. The condenser water flows through the condenser of the chiller. The condenser is also a heat exchanger. In this case the heat absorbed from the building, plus the work of compression, leaves the refrigerant (condensing the refrigerant) and enters the condenser water (raising its temperature). The condenser has the same limitations to flow change as the evaporator. Chillers and Energy Efficiency. Chillers are often the single largest electricity users in a building. A 1. 00. 0 ton chiller has a motor rated at 7. Improving the chiller performance has immediate benefit to the building operating cost. Chiller full load efficiency ratings are usually given in the form of k. W/ton, COP (Coefficient of Performance = k. Wcooling / k. Winput) or EER (Energy Efficiency Ratio = Tons X 1. Winput). Full load performance is either the default ARI conditions or the designer specified conditions. It is important to be specific about operating conditions since chiller performance varies significantly at different operating conditions. Chiller part load performance can be given at designer- specified conditions or the NPLV (Non- Standard Part Load Value) can be used. The definition of NPLV is spelled out in ARI 5. Test Standard for Chillers. For further information refer to Mc. Quay Application Guide AG 3. Centrifugal Chiller Fundamentals. Chiller full and part load efficiencies have improved significantly over the last 1. Chillers with NPLVs of 0. W/ton are available) to the point where future chiller plant energy performance will have to come from chiller plant design. ASHRAE Standard 9. Table 6. 2. 1. C of this standard covers chillers at ARI standard conditions. Tables 6. 2. 1. H to M cover centrifugal chillers at non- standard conditions. Copyright 2. 00. 1, American Society Of Heating, Air- conditioning and Refrigeration Engineers Inc., www. Reprinted by permission from ASHRAE Standard 9. Piping Basics. Static Pressure. Figure 3 - Closed Loop. The piping is usually steel, copper or plastic. The chilled water piping is usually a closed loop. A closed loop is not open to the atmosphere. Figure 3 shows a simple closed loop with the pump at the bottom of the loop. Notice that the static pressure created by the change in elevation is equal on both sides of the pump. In a closed loop, the pump needs only to overcome the friction loss in the piping and components. The pump does not need to . Condenser pump must overcome the friction of the system and . Figure 4 shows an open loop. Notice the pump need only overcome the elevation difference of the cooling tower, not the entire building. This should be consideredcarefully for buildings over 1. In high- rise applications, the static pressure can become considerable and exceed the pressure rating of the piping and the components such as chillers. Although chillers can be built to higher pressure ratings (The standard is typically 1. PSI but the reader is advised to check with the manufacturer) high pressure systems can become expensive. The next standard rating is typically 3. PSI. Above that, the chillers become very expensive. One solution is to use heat exchangers to isolate the chillers from the static pressure. While this solves the pressure rating for the chiller, it introduces another device and another approach that affects supply water temperature and chiller performance. A second solution is to locate chiller plants on various floors throughout the building selected to avoid exceeding the 1. PSI chiller rating. Figure 4 - Open Loop. Expansion Tanks. An expansion tank is required in the chilled water loop to allow for the thermal expansion of the water. Expansion tanks can be open type, closed type with air- water interface or diaphragm type. Tank location will influence the type. Open tanks must be located above the highest point in the system (for example, the penthouse). Airwater interface and diaphragm type tanks can be located anywhere in the system. Generally, the lower the pressure in the tank, the smaller the tank needs to be. Tank size can be minimized by locating it higher in the system. Figure 5 - Expansion Tank Location. The pressure at which the tank is operated is the reference point for the entire hydronic system. The location of the tank - which side on the pump (suction or discharge) - will affect the total pressure seen by the system. When the pump is off, the tank will be exposed to the static pressure plus the pressure due to thermal expansion. If the tank is located on the suction side, when the pump is running, the total pressure seen on the discharge side will be the pressure differential, created by the pump, added to the expansion tank pressure. If the expansion tank is located on the discharge side of the pump, the discharge pressure will be the same as the expansion tank pressure and the suction side pressure will be the expansion tank pressure minus the pump pressure differential. Piping Insulation. Chilled water piping is insulated since the water and hence the piping is often below the dewpoint temperature. Condensate would form on it and heat loss would occur. The goal of the insulation is to minimize heat loss and maintain the outer surface above the ambient air dewpoint. Condenser Water Piping. In most cases, the condenser water piping is an open loop. Figure 4 shows an open loop with the water open to the atmosphere. When the pump is not running, the level in the supply and return piping will be even at the level of the sump. When the pump operates, it needs to overcome the friction loss in the system and . Condenser water piping is typically not insulated since there will be negligible heat gain or loss and sweating will not occur. If the piping is exposed to cold ambient conditions, however, it could need to be insulated and heat traced to avoid freezing. Reverse Return/Direct Return Piping. Figure 6 - Reverse Return Piping. Figure 6 shows reverse return piping. Reverse return piping is designed such that the path through any load is the same length and therefore has approximately the same fluid pressure drop. Reverse return piping is inherently self- balancing. It also requires more piping and consequently is more expensive. Figure 7 - Direct Return Piping. Direct return piping results in the load closest to the chiller plant having the shortest path and therefore the lowest fluid pressure drop. Depending on the piping design, the difference in pressure drops between a load near the chiller plant and a load at the end of the piping run can be substantial. Balancing valves will be required. The advantage of direct return piping is the cost savings of less piping. For proper control valve selection, it is necessary to know the pressure differential between the supply and return header (refer to Control Valve Basics, page 2. While at first it would appear with reverse return piping, that the pressure drop would be the same for all devices, this is not certain. Changes in pipe sizing in the main headers, different lengths and fittings all lead to different pressure differentials for each device. When the device pressure drop is large relative to piping pressure losses, the difference is minimized. In direct return piping, the pressure drops for each device vary at design conditions depending on where they are in the system. The valve closest to the pumps will see nearly the entire pump head. Valves at the furthest end of the loop will see the minimum required pressure differential.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
August 2017
Categories |