Edition No. 14 December 2002 ENGINEERING

1 Continued from previous page continued from previous page performance so it can be expected that the chiller operating conditions. Said another way; the best pressure drops will not decrease with increased temper- McQuay solution may not necessarily be the best ature ranges. In addition, the passes will increase (two solution for other chiller vendors and vice-versa. pass to three pass) as the range increases. All chillers are negatively affected by increased compressor Edition No. 14 December 2002. chiller types, differentiated by compressor or manu- lift. Some chiller types (screw chillers, for instance) are facturer, were not considered. While it is true that all chillers will behave generally the same, the specific properties of a chiller will change the outcome.

2 chiller plant types will also affect the outcome. As the chilled water temperature range is increased, series chillers will outperform either a single large chiller or less affected. Casually increasing the compressor lift for any chiller type or manufacturer will increase the operating cost. Changing the temperature ranges and supply temperatures requires careful analysis. The following are some points to consider: The traditional ARI operating conditions work ENGINEERING . S Y S T E M S O L U T I O N S. parallel chillers. Series counterflow chillers will very well for many buildings. outperform series chillers; however, the savings may be Unnecessary reduction of the chilled water supply Why Change the Chilled T. lost when considering the condenser pump work.

3 Temperature should be avoided because it increases his issue of ENGINEERING Pump head is a key parameter. Increasing the pump chiller work. System Solutions is on head will make the pump work more dominant and change the outcome. When using standard products such as fan coils and unit ventilators, maintain the chilled water chilled and condenser water temperature ranges. There is a Water Temperature Range? Conclusion temperature range between 10 and 12 F where To answer this question, let's review the primary goal of HVAC design. The they are designed to operate. fair amount of information Temperature ranges are a complicated issue. There is no goal is to provide the customer with a safe, comfortable environment at an single best solution that can be used for every case.

4 Each Increasing the chilled water temperature range is a circulated these days on the best acceptable life cycle cost. Focusing on life cycle cost brings up the necessary project will have its own optimum operating conditions. good way to reduce the capital and pump For comments or suggestions, please call or write: temperature ranges to use. Some of balance between capital cost and operating cost. It is here that changing the Chris Sackrison, Editor To further complicate matters, different chillers (either operating cost, particularly if the pump head is McQuay International the information is good, some not, as chilled water temperature range becomes an issue. To consider the capital cost, types or manufacturers) will have their own optimum large or the piping runs long.

5 13600 Industrial Park Boulevard let's look to the following formula: Minneapolis, MN 55441 it was true in the refrigerant wars . continued on back page Phone: (763) 553-5419 Load (tons) = Flow (US gpm) x Temperature range ( F)/24. E-mail: of the 1990s. The topic is For more information on McQuay products and services, or to speak with your local representative, call (800) 432-1342, or visit our web page at or McQuay Air- cooled Chillers 2002 McQuay International complicated; changing the chilled water temperature will affect every Flow (US gpm) = Load (tons) x 24/ Temperature Range ( F). As the chilled water temperature range is increased, the flow rate is decreased component in the cooling HVAC. High Efficiency And Low Noise At An Affordable Price for the same capacity.

6 Smaller flow means smaller pipes, pumps, insulation system. (area not R value), etc. This equates to capital savings. Notice that the chilled McQuay air- cooled scroll compressor chillers are the Flexible Options to Meet Your Needs water supply temperature is not part of the equation. It has nothing to do with complete, factory-assembled solution for your HVAC McQuay offers you the flexibility to choose from many This article attempts to show the these savings! requirements. Our 10 to 130-ton chillers are loaded with sizes and options to customize your air- cooled scroll relationships between the To evaluate the operating cost, let's consider the following formula: value-added features at an affordable price. compressor chiller . components that make up the air Pump power (hp) = [Flow (US gpm) x Head (ft)] / [3960 x Pump efficiency].

7 Efficient Meets or exceeds ASHRAE Standard Low ambient operation down to 0 F. conditioning system so that the (October 2001). Up to EER at full load, and up As the chilled water flow is decreased, the pump work is also decreased, Non-fused disconnect switches allow secure and easy reader can appreciate the nuances. assuming constant head. This equates to operating savings. Notice again that to EER at part load (IPLV). service. There is no one solution, no perfect chilled water supply temperature has nothing to do with the savings. Quiet All dBA ratings are tested in accordance with Phase voltage monitor senses and avoids undesirable ARI Standard 370. Less acoustical treatment lowers operating condition that will yield The pump head will remain approximately constant because the pipe sizes will electrical conditions.

8 Be decreased. ASHRAE recommends that piping design be based on a 4-foot your project's cost. the best result for any and all Ice storage capability saves energy. pressure drop per 100 feet of pipe. Reliable Tandem or trio scroll compressor sets per buildings. The only absolute Maintaining this requirement will let Double evaporator insulation for ice storage operation. circuit have fewer moving parts. Two circuits at 26 answer is that, unless it is backed up the designer downsize piping as the tons provide backup chilled water. Several options are Condenser coil options provide longer equipment life (copper fins, Electrofin and Blackfin coating). with an energy analysis specific to flow decreases. available to enhance performance and reliability.

9 Hot gas bypass for low load operation. your application, care should be Consider the Entire System Controls Flexibility Protocol Selectability allows The two considerations discussed MicroTech II DDC controls to easily integrate into Acoustical blanket wraps compressor for reduced exercised. above are two very strong arguments your building automation system of choice. And it's sound transmission. for increasing the chilled water simple to achieve interoperability using open, standard For more information on air temperature range. These protocols such as LonTalk or BACnet . conditioning system design, contact considerations, however, are only your local McQuay representative or focused on the pumps and piping. visit Designers must consider the entire HVAC system and changing the Hugh Crowther chilled water temperature range will Director of Applications affect the entire system!

10 McQuay North America Continued on next page. Figure 1 chiller Heat Exchangers at ARI Conditions AGZ-A. (10 to 39 tons) AGZ-B. (26 to 130 tons). Starting with the chiller constant. However, if the supply water temperature is Increasing the condenser water temperature range will reduce over $90/kW). This location should favor HVAC systems The purpose of a chiller is to collect heat from the chilled lowered, then the refrigerant boiling temperature will have the condenser pump, pipe and cooling tower sizes, saving with the lowest peak power performance. Again, the annual water loop and reject it in the condenser water loop. This to be lowered. This will increase the compressor lift (See capital costs. On the other hand, it will result in some performance suggests the chilled water temperature ranges Moral: process takes work, so a compressor is required.