Table of Contents Part I: The Basic Tools Part II: HVAC Pumps and Their Performance Part III: The HVAC World Part IV: Pumps for Open HVAC Cooling Systems Part V: Pumps for Closed HVAC Cooling Systems Part VI: Pumps for HVAC Hot Water Systems Part VII: Installing and Operating HVAC Pumps SUMMARY OF HVAC ENERGY EVALUATIONS Chapters DIGITAL ELECTRONICS AND HVAC PUMPS PHYSICAL DATA FOR HVAC SYSTEM DESIGN PIPING SYSTEM FRICTION BASICS OF PUMP DESIGN PHYSICAL DESCRIPTION OF HVAC PUMPS HVAC PUMP PERFORMANCE PUMP DRIVERS AND VARIABLE-SPEED DRIVES THE USE OF WATER IN HVAC SYSTEMS CONFIGURING AN HVAC WATER SYSTEM 10 BASICS OF PUMP APPLICATION FOR HVAC SYSTEMS 11 OPEN COOLING TOWER PUMPS 12 PUMPS FOR PROCESS COOLING 13 PUMPING OPEN THERMAL STORAGE TANKS 14 CHILLERS AND THEIR PUMPS 15 CHILLED WATER DISTRIBUTION SYSTEMS 16 CLOSED CONDENSER WATER SYSTEMS 17 PUMPS FOR CLOSED ENERGY STORAGE SYSTEMS 18 PUMPS FOR DISTRICT COOLING AND HEATING 19 STEAM AND HOT WATER BOILERS 20 LOW-TEMPERATURE HOT WATER HEATING SYSTEMS 21 PUMPS FOR MEDIUM- AND HIGH-TEMPERATURE WATER SYSTEMS 22 CONDENSATE, BOILER FEED, AND DEAERATOR SYSTEMS 23 INSTRUMENTATION AND CONTROL FOR HVAC PUMPING SYSTEMS 24 TESTING HVAC CENTRIFUGAL PUMPS 25 INSTALLING HVAC PUMPS AND PUMPING SYSTEMS 26 FACTORY-ASSEMBLED PUMPING SYSTEMS 27 OPERATING HVAC PUMPS 28 MAINTAINING HVAC PUMPS 29 RETROFITTING EXISTING HVAC WATER SYSTEMS 30 SUMMARY OF HVAC ENERGY EVALUATIONS 31 THE MODERN TWO-PIPE HEATING AND COOLING SYSTEM 31 ADVANCED HEAT RECOVERY Source: HVAC Pump Handbook Part The Basic Tools Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website The Basic Tools Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Source: HVAC Pump Handbook Chapter Digital Electronics and HVAC Pumps 1.1 Introduction The emergence of digital electronics has had a tremendous impact on industrial societies throughout the world In the heating, ventilating, and air-conditioning (HVAC) industry, the development of digital electronics has brought an end to the use of many mechanical devices; typical of this is the diminished use of mechanical controls for HVAC air and water systems Today’s digital control systems, with built-in intelligence, more accurately evaluate water and system conditions and adjust pump operation to meet the desired water flow and pressure conditions Drafting boards and drafting machines have all but disappeared from the design rooms of heating, ventilating, and air-conditioning engineers and have been replaced by computer-aided drafting (CAD) systems Tedious manual calculations are being done more quickly and accurately by computer programs developed for specific design applications All this has left more time for creative engineering on the part of designers to the benefit of the client 1.2 Computer-Aided Calculation of HVAC Loads and Pipe Friction The entire design process for today’s water systems, from initial design to final commissioning, has been simplified and improved as a result of the new, sophisticated computer programs One of the most capable programs for sizing and analyzing flow in fluid systems is the piping systems analysis program developed by APEC, Inc (Automated Procedures for Engineering Consultants), headquartered in Dayton, Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Digital Electronics and HVAC Pumps The Basic Tools Ohio APEC, a nonprofit, worldwide association of consulting engineers and in-house design group, is dedicated to improving quality and productivity in the design of HVAC air and water systems through the development and application of advanced computer software The APEC PSA-1 program accurately calculates the friction losses and sizes of pipes as well as simulating flow under different operating conditions in either new or existing piping systems Analyzing the fluid flow in systems with diversified loads, multiple pumps, and chillers or boilers is essential if engineers are to truly understand the real operating conditions of large HVAC water systems This understanding can only be achieved through the use of a computer program capable of such thorough analysis 1.2.1 Typical input for APEC piping system analysis program The following is representative system data into an APEC’s computer program for calculating pipe sizing, friction, and flow analysis, and typical output Master Data files Pipe, fitting, and valve files Material friction loss Actual ID for nominal copper type (M,L) Steel schedule other Standard pipe pre-entered or custom Cost estimation optional Insulation file Type K value Thickness Cost estimation optional Fluids Provisions for all fluid types with: Density Temperature Viscosity Specific heat System data Pipe environment Required for heat/loss gain Space temperature Outside air temperature Soil conductivity Burial depth Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Digital Electronics and HVAC Pumps Digital Electronics and HVAC Pumps Program options System sizing Flow simulation Cost estimate Flow simulation options-typical entries Maximum iterations 30 Intermediate results Every iterations Temperature tolerance for convergence 0.50 Relaxation parameters 0.50°F Fill pressure 46 ft of head (or H2O) Pump data Variable or constant speed Points for pump curves Terminal data (coils, etc.) Fluid flow Pressure drop Coil cfm (ft3/min) Inlet air temperature Leaving air set point Valve data Valve coefficient Trial setting Valve control 1.2.2 Typical output for APEC piping system analysis program Table 1.1 includes samples of output headings, with one line of output for only three output forms available The output also has forms that mirror the input, so the designer has a complete record of the entire analysis This program is now being expanded to include many additional piping features and to accommodate contemporary computer practices such as Windows, to speed the development and manipulation of project data Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Digital Electronics and HVAC Pumps The Basic Tools TABLE 1.1 Sample Output Headings Pressure-drop analysis* Node Pipe From To Diameter Length, ft Pipe PD 2.50 22.5 0.75 Terminal Flow PD CV PD 70 22 31.0 Fitting Special Total PD PD PD 0.21 53.96 System estimate† Material Labor Item Size Description Quantity Unit Unit Cost Unit Cost Total Cost 2.00 Schedule 40 115.0 LF 2.42 278 42 4830 5108 Final simulation results Link Start End Pipe diameter 2.5 Flow (gpm) Pressure head (ft) Input Actual At start Node Temperature, °F 70 75.3 34.4 (79.37) 160 *Chiller or boiler pressure drop not included †Labor and cost units are entered by user as master data for given localities Cost estimates are not intended to give accurate costs for bidding purposes 1.3 Hydraulic-Gradient Diagrams The hydraulic-gradient diagram provides a visual description of the changes in total pressure in a water system To date, these diagrams have been drawn manually; the actual drawing of the hydraulicgradient diagram is now being evaluated for conversion to software; when this is completed, the diagram will appear automatically on the computer screen after the piping friction calculations are completed The hydraulic-gradient diagram has proved to be an invaluable tool in the development of a water system It will appear throughout this book for various types of water systems Its generation will be explained in Chap Clarification should be made between an energy gradient and the hydraulic gradient of a water system The energy gradient includes the velocity head V 2/2 g, of the water system, while the hydraulic gradient includes only the static and pressure heads Velocity head is usually a number less than ft and is not used to move water through pipe, as are static and pressure heads Using the energy gradient with the velocity head increases the calculations for developing these diagrams; therefore, the hydraulic gradient is used instead 1.3.1 Energy and hydraulic gradients Figure 1.1 describes the difference between the energy gradient and the hydraulic gradient This diagram is typical for an open system Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Digital Electronics and HVAC Pumps Digital Electronics and HVAC Pumps Figure 1.1 Energy and hydraulic gradients (From Karassik et al., Pump Handbook, 3rd ed, McGraw-Hill, used with permission.) such as an open cooling tower circuit; the closed systems of HAVC including chilled and hot water systems consist of a loop, since the water returns to its source The individual losses in a water system are explained in this diagram Velocity head cannot be ignored, since it represents the kinetic energy of the water in the pipe Velocity head will be emphasized in this book when it becomes a factor in pipe design, particularly in piping around chillers and in the calculation of pipe fitting and valve losses 1.4 Speed and Accuracy of Electronic Design of Water Systems The tremendous amount of time saved by electronic design enables the engineer to evaluate a water system under a number of different design constraints The designer can load certain design requirements into a computer, and while the computer is doing all the detailed calculations for that program, the next program of design considerations Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Digital Electronics and HVAC Pumps The Basic Tools can be set up for calculations by the computer After all the programs have been run, the designer can select the one that provides the optimal system conditions that meet the specifications of the client The designer now has time to play “what if ” to achieve the best possible design for a water system In the past, the engineer was often time driven and forced to utilize much of a past design to reach a deadline for a current project Now the engineer can model pumping system performance under a number of different load conditions and secure a much more complete document on the energy consumption of proposed pumping systems The designer can compute the diversity of an HVAC system with much greater accuracy Diversity is merely the actual maximal heating or cooling load on an HVAC system divided by the capacity of the installed equipment For example, assume that the total cooling load on a chilled water system is 800 tons, but there are 1000 tons of cooling equipment installed on the system to provide cooling to all parts of that system This disparity is caused by changing some loads or differences in occupancy The diversity in this case would be 800/1000, or 0.80 (80 percent) This is a simpler and easier definition of diversity than a more technical definition that states that diversity is the maximal heating or cooling load divided by the sum of all the individual peak loads For example, a 10-ton air handler might have a peak load of only 9.2 ton The true diversity might be slightly less than that acquired by using the installed load 1.4.1 Equation solution by computer A number of equations are provided herein for the accurate solution of pressures, flows, and energy consumptions of HVAC water systems These equations have been kept to the algebraic level of mathematics to aid the HVAC water system designer in the application of them to computer programs Computer software is now available commercially to assist in the manipulation of these equations Typical of them is the EES —Engineering Equation Solver program, available from FChart Software, Middleton, Wis 1.5 Databasing After the designer has completed the overall evaluation of a water system, databasing can be used to search elements of past designs for use on a current project Databasing is a compilation of information on completed designs in computer memory that can be recalled for Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website The Modern Two-Pipe Heating and Cooling System 628 Installing and Operating HVAC Pumps Figure 31.5 × Pipe changeover variations in supply water to the two-pipe side versus the 4-pipe side The modulating valve can also be used to slowly regulate the changeover to ensure safe water temps at the chiller or boiler In a couple of cases where chilled water delta-T was a concern of the owner, a temperature transmitter in the return line was used to control pump speed That arrangement will work if the building is proportionally balanced, but it assumes that all spaces served by the two-pipe are relatively equally loaded The two-pipe geothermal system is recent synthesis of three technologies that separately have proven to be very effective From two-pipe comes economy and simplicity for school designs, and the proven ability to heat large buildings with low temperature water From geothermal comes a very efficient heating and cooling sink And from heat recovery chillers comes a proven machine that can be programmed to make 44°F cooling water and 130°F heating water Natural gas energy prices post–Hurricane Katrina (2005 super storm) may finally be the tipping point that will offset what has been an unjustifiably high cost of the geothermal well field It is important to note that this arrangement is not a heat pump Heat pumps cannot handle cold winter air or humid summer air effectively, and most are equipped with a decoupled makeup air system, a big first cost penalty Because they cannot handle outside air, heat pumps cannot run economizer cooling, which is a severe operating cost penalty in a school Two-pipe geothermal can operate air side economizers and it can use the ground temperature to cool the building when the ground temperature and dew point allow Figure 31.6 shows the three water flow arrangements Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Figure 31.6 Two-pipe geothermal The Modern Two-Pipe Heating and Cooling System 629 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website The Modern Two-Pipe Heating and Cooling System 630 Installing and Operating HVAC Pumps 31.11 Conclusions Over 150 successful installations have shown that for the right application, a properly designed modern two-pipe system will be less expensive to build, less expensive to operate, and easier to maintain than any other HVAC option If designed and operated properly, there will be no compromises in indoor air quality, occupant comfort, or humidity control Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Source: HVAC Pump Handbook Chapter 32 Advanced Heat Recovery 32.1 Introduction There are several references to heat recovery herein, but a detailed review of the latest activities in this field is provided in this chapter where it can be discussed extensively The largest source of heat for recovery in the HVAC industry is the heat rejection from chillers Another source of heat is flue gases emanating from all types of boilers The development of the condensingtype boiler has all but eliminated the hot water boiler as a source of heat for recovery since much of the water vapor from combustion is condensed already Steam boilers can be sources of heat recovery from flue gases, and the cost of fuels may provide the impetus to evaluate the economics of economizers on the stack connections of them For the most part, this chapter will be devoted to the evaluation of heat rejection from chillers It is recognized that there are other possibilities outside the HVAC industry As was calculated in Chap 11, there is a sizeable amount of heat to be recovered from chiller condensers The costs of heat recovery were not conducive to so in the past New equipment, digital control, and sensible selection of operating temperatures have resulted in heat recovery that does make economic sense No longer is it viewed as necessary to have 180 to 200°F water to heat 78°F air The use of 130°F water for heating will increase the size and cost of the heating coil on a four-pipe heating and cooling system However, the ability to use a condensing boiler with thermal efficiencies above 90 percent usually amortizes this extra cost within an acceptable period of operation Such a cost analysis should be conducted on a jobto-job basis to confirm the amortization period Standard procedures are available for making these cost analyses 631 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 632 Installing and Operating HVAC Pumps 32.2 The Logic of Heat Recovery Is it logical to have a source of heat injected into a building when an appreciable amount of heat is being rejected from that building? We have to find a way to use the Second Law of Thermodamics to move heat from a warmer source to a cooler receiver In the past, the needed heat requirements were too high in temperature and the waste heat was too low Now that we are correcting this imbalance, we can proceed to develop systems that will enable us to recover the heat from chiller condensers and reduce appreciably the needed heat from boilers or direct fired air heaters The basic rule of heat recovery then is to use recovered heat wherever economically possible before consuming electricity or fossil fuels 32.3 Types of Heat Recovery Chillers There are three types of water-cooled chillers when classifying them as to the configuration of their condensers Most of the contemporary chillers are designed to reject their heat at temperatures around 95°F; others are dedicated to be heat recovery chillers with condenser water leaving temperatures of around 130°F, and the third type have double bundle condensers with one tube bundle designed to provide the heat recovery The coefficient of performance (COP) of the heat recovery chiller, when counting the cooling only, is not as high as the very efficient chillers now operating with standard leaving condenser water temperatures The problem with the double-bundle condenser is the inability to provide a correct ratio between the conventional condenser and the needed amount of heat recovery The result is the emergence of the dedicated heat recovery chiller (DHRC) that is available in a number of sizes and can be furnished in modules as needed for heat recovery load Typical construction of the DHRC is shown in Figs 32.1 and 32.2 32.4 Heat Available from Chillers The heat available from a chiller is the 12,000 Btu per ton-hour plus the thermal equivalent of the energy consumed which, for electricity, is 3412 Btu/kW Equation 32.1 provides this Heat available for recovery ϭ 12,000 + (kW/ton ⋅ 3412) Btu/ton-hour (32.1) The ton-hour is equivalent to 12,000 Btu; the current kilowatts per ton for contemporary water-cooled chillers is around 0.6 or Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery Advanced Heat Recovery Figure 32.1 633 Exterior view of DHRC (Courtesy of Multistack, West Salem, WI.) approximately 2000 Btu For general calculation purposes, the heat available per ton from the water-cooled chiller would be 14,000 Btu per ton-hour For precise calculation, the actual kilowatts per ton for the chiller should be determined for the operating range of the chiller when heat is being recovered Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 634 Installing and Operating HVAC Pumps Figure 32.2 Interior view of DHRC (Courtesy of Multistack, West Salem, WI.) 32.5 Instrumenting a Dedicated Heat Recovery Chiller (DHRC) Figure 32.3 describes the instrumentation of this chiller Since energy is being measured, quality temperature and flow transmitters should be utilized to secure accuracy in the measurements In particular, repeatability should be emphasized so that the operators can depend on these measurements for their operation of the chiller plant Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery Advanced Heat Recovery To heat recovery 635 Supply chilled water t4 t1 From heat recovery f2 Evaporator Condenser kW C t3 DHRC t2 f1 From HX Return chilled water Figure 32.3 Instumentation for dedicated heat recov- ery chiller The flow and temperature measurements are as follows: Chilled water flow, gal/min f1 Condenser water flow, gal/min f2 Chilled water return temperature °F t2 Chilled water supply temperature °F t1 Condenser entrance temperature °F t3 Condenser leaving temperature °F t4 It should be noted that the condenser entrance temperature and flow transmitters are installed before any return water from the cooling tower is mixed with the water from the heat recovery processes 32.6 Typical Piping for the DHRC Figure 32.4 provides the typical piping for DHRC; the use of the heat recovery will be shown in other figures The DHRC can be piped in series or parallel with the other chillers Valve V1 can be furnished if there may be a reason for both series and parallel operation Valve V2 provides connection to a cooling tower, heat exchanger or closed-circuit cooler in event that the condenser heat is greater than that needed for the heat recovery processes The pumping requirements for operating the DHRC in parallel with other chillers can vary from no pump needed to one with sizeable Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 636 Installing and Operating HVAC Pumps From chillers Chilled water To chillers DHRC condenser pumps V1 t4 f1 f2 C Evaporator Condenser Heat recovery DHRC t3 V2 HX To cooling tower or closed circuit cooler DHRC chilled water pumps t1 t2 Figure 32.4 Typical piping for dedicated heat recovery chiller head; this is determined by the actual configuration of the central chilled water plant Seldom is an open cooling tower connected directly with the DHRC; the heat recovery circuit should be closed through the use of a heat exchanger with a cooling tower or a closed-circuit cooler 32.7 Heat Recovery Equations The basic equations for heat recovery are quite simple; assuming the specific heat of water to be 1.0 and the density to be 8.33 lb/gal, the multiplier for the product of the flow times the temperature difference is 500 So Heat recovered ϭ 500 ⋅ f2 (t4 − t3) Btu/h (32.2) The simultaneous generation of chilled water in tons is Tons of cooling 500 # f1 st2 t1d 0.125 # f1 st2 t1d tons 12,000 (32.3) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery Advanced Heat Recovery 637 The total COP for the electric motor driven, heat recovery chiller is a sum of the above two equations in British thermal unit per hour divided by the thermal equivalent of the kW input to the chiller Total COP 500 [f2 st4 t3d f1 st2 t1d] kW # 3412 0.147 [f2 st4 t3d f1 st2 t1d] (32.4) Following is actual data derived from a 50-ton DHRC: Chilled water flow f1 ϭ 100 gal/min; condenser flow f2 ϭ 81 gal/min Chilled water temperatures: t2 ϭ 56°F; t1 ϭ 44°F Condenser water temperatures: t4 ϭ 130°F; t3 ϭ 110°F kW input ϭ 62 kW Inserting these values in Eq 32.4 provides the total COP for the chiller Total COP 0.147[100s56 44d 81s130 110d] 6.7 62 These are the basic equations for heat recovery from chillers They can be adapted to the various uses of recovered heat 32.8 The Uses of Recovered Heat Recovered heat from chillers can be used for (1) domestic water heating, (2) space heating, (3) heat recovery reheat in VAV boxes or airhandling units, and (4) any other process where the heat receiver is lower in temperature than the leaving temperature t4 of the DHRC The use that has the lowest temperature will be the most economical since the leaving water temperature, t4, of the chiller condenser will also be the lowest for any of these uses Usually, this is domestic water heating 32.8.1 Domestic water heating Domestic water heating is an excellent use for recovered heat due to its relatively low supply temperatures, namely, 45 to 55°F This is the first use that should be considered for recovered heat Heat recovery for domestic water heating can reduce substantially the operation of hot water boilers in the summertime Figure 32.5 describes the typical Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 638 Installing and Operating HVAC Pumps Warm domestic water From chillers Chilled water To chillers ´ DHRC condenser pumps Cold domestic water Double coil heat exchanger f2 Condenser Heat recovery Circulator V1 t4 t3 V2 HX C Evaporator Storage tank DHRC DHRC chilled water pumps t1 t2 To cooling tower or closed circuit cooler Figure 32.5 Domestic water piping for heat recovery piping arrangement for the use of heat recovery for domestic water heating The heat exchanger must be double-wall construction to prevent the flow of condenser water into the domestic water Usually, a storage tank is provided for the domestic water to account for variations in domestic water demand and availability of recovered heat Circulating pumps move the condenser water through the chiller condenser to the domestic water heat exchanger The great advantage for domestic water heating is the fact that the DHRC can operate with a lower condenser water temperature and a lower kilowatts per ton Combining this fact with the recovered heat yields a much higher COP For example, with 72 gal/min of condenser water circulating through the domestic water heat exchanger, the overall COP for the above example becomes COP 500[100s56 44d 72s90 70d] 11.4 34 # 3412 In this case, the actual useful heat is greater for the domestic water, 720 MBH, than the thermal equivalent for the chilled water, 600 MBH Not included in this calculation is the reduction in cooling tower energy and maintenance costs, since the cooling tower flow has been reduced from around 100 gal/min to less than 40 gal/min Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery Advanced Heat Recovery 639 A particularly attractive application is an installation of air-cooled chillers operating with a COP of 2.9 If the available tonnage of the chiller plant is 250 tons, the above DHRC could increase substantially the COP of the entire plant With 200 tons furnished by the air-cooled chillers and 50 tons by the DHRC, the overall COP would be increased as follows: Overall COP 200 # 2.9 50 # 11.4 4.6 250 The addition of the DHRC in this case increases the overall COP from 2.9 to 4.6 It is apparent from these calculations that the heat recovery process must be in operation to achieve this high coefficient of performance 32.8.2 Other uses for recovered heat To heating or reheat coils All other uses for recovered heat have condenser water from the DHRC in the heating coils, Fig 32.6 Since the cooling tower has a From chillers Chilled water Boiler To chillers DHRC ´ condenser pumps 90°F f2 C Evaporator t1 Condenser 130°F Hot water pump V1 t4 t3 V2 HX DHRC DHRC chilled water pumps f1 t2 To cooling tower or closed circuit cooler Figure 32.6 Heat recovery for heating or heat recovery coils Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 640 Installing and Operating HVAC Pumps heat exchanger or is a closed-circuit cooler, there is no difference in the chemistry of the DHRC condenser water and the hot water for heating Therefore, this condenser water can be used in the heating coils These heating coils include those for space heating as well as for reheat Another application of recovered heat is in natatorium air handling units Since natatoriums require dehumidification year round, the latent heat can be recovered for reheat and heating the pool water or other parts of the building 32.9 Sizing the DHRC How large should the DHRC be, in comparison to the regular chillers on a particular installation? The heat recovery chiller should be designed to accommodate as much of the heating load as economically possible Remember that for every ton of cooling, 14,000 Btu is available for heating The basic rule for sizing the DHRC is as follows 32.9.1 Prevent boilers from running in the summer and main chillers in the winter The first step is to make a detailed analysis of the summer heating loads, which in most cases, are domestic water heating and reheat in air-handling units and VAV boxes The instantaneous domestic water heating load can be reduced through the installation of a hot water storage tank The sizing of this tank must take in to consideration the availability of space for it and the need to keep it warm when there is neither heating nor cooling loads in the building A very careful study should be made of both domestic water and reheat requirements in the sizing of the DHRC Winter cooling requirements of the building should determine the size of the DHRC In this case, the heat from the condenser can be used to heat partially the domestic water load or to reduce the heating load on the boilers It is obvious that this is a complex problem needing great care in its solution One characteristic that the DHRC has is the ability to be installed in modules so that it is not difficult to install additional tonnage if the initial installation proves to be inadequate The space provided for the DHRC should be adequate in event that this addition is required 32.10 Control of DHRC It is obvious that the control of heat recovery chillers is different from that for ordinary chillers The control of the condenser heat becomes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery Advanced Heat Recovery 641 the principal objective of the control system as well as the needed production of a specific number of tons of cooling or a chilled water supply temperature For example, several of the piping configurations discussed earlier assume that no heat is being rejected to a cooling tower or other heat absorbing equipment How can this be done? With many applications of these chillers, the desire is to produce a specific amount of heat from the condenser, and the cooling effect is secondary To achieve this, it is necessary to control the chiller operation by the amount of heat that is derived from the chiller This can be done by maintaining a particular water temperature for the water leaving the condenser Other applications may require the control of the water temperature entering the condenser As has been stated repeatedly, the DHRC makes sense when there is a simultaneous need for heating and cooling, and it must run as many hours as possible Further to that point, when the DHRC is operating to satisfy the facility’s hot water requirements, there must be a chilled water requirement in the building that meets or exceeds the hot water demand If this is not the case, the heat recovery system will subcool the chilled water loop and eventually shut down automatically on a low temperature fault Similarly, if the DHRC is operating to satisfy the facility’s chilled water requirement, there must be a hot water requirement in the building that meets or exceeds the chilled water demand It has been discovered that the best way to operate the DHRC is to always set the control point (hot water or chilled water) to the side of the system that has the lowest demand In doing this, we are always assured of operating the heat recovery system during the maximum available hours for maximum economic impact on the facility This can be done by simply monitoring the temperatures on the side of the system (hot water or chilled water) that is not being actively controlled by the DHRC That is, if the chiller is controlling to a leaving hot water temperature, thus producing chilled water as a by-product, then the control system must monitor the entering chilled water temperature If this temperature drops below a predetermined set point, indicating a lack of chilled water load, the control point of the DHRC is changed over to the chilled waterside of the system This will ensure that the heat recovery system will only produce the amount of heat that can safely be absorbed from the facility’s chilled water system This logic would then be applied similarly when in the chilled water control mode This control may be easily accomplished by the building control system or can come prepackaged within the DHRC control system Such chillers are being produced now with automatic switchover from control of the amount of cooling to the amount of heat recovered Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website Advanced Heat Recovery 642 Installing and Operating HVAC Pumps 32.10.1 Operator training Actual installations of these chillers have proved the need to train the chiller plant operators to understand the need to operate the heat recovery chillers as many hours as possible Likewise, the owners and managers of these chillers must understand the operation of these chillers to ensure that they operate as many hours per year as possible 32.11 Summary Recovering heat from water-cooled chillers is an important effort today, and it will become more urgent as the cost of electricity and fossil fuels increases There are a number of dedicated heat recovery chillers now operating that should provide adequate references for the design engineer to verify the preceding information for a potential application This is an excellent subject to close this book on HVAC pumping and Energy Conservation in the HVAC Industry Much has been provided on new technology now available to improve the application of pumps Table 32.1 provides a list of barriers that can deter the use of this technology These statements should assist us as we progress toward optimum use of energy in the HVAC world Table 32.1 Barriers Identified to Best Practices An overall reluctance to change The perception that utilizing high-performance HVAC equipment and sources increase initial costs Retrofit opportunities are often postponed due to up-front costs Expectations are often unrealistic The demands for verification can be unrealistic Standard practices are not questioned or reevaluated in light of new technologies Perceived or actual liability Codes and standards may discourage innovative solutions Poor ratings systems (e.g., boilers) may obscure actual efficiency differences SOURCE: Energy efficiency and renewable energy, Thomas H Durkin, PE Director of Engineering, Veazey Parrott Durkin and Shoulders Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website ... CONTROL FOR HVAC PUMPING SYSTEMS 24 TESTING HVAC CENTRIFUGAL PUMPS 25 INSTALLING HVAC PUMPS AND PUMPING SYSTEMS 26 FACTORY-ASSEMBLED PUMPING SYSTEMS 27 OPERATING HVAC PUMPS 28 MAINTAINING HVAC PUMPS... website Source: HVAC Pump Handbook Chapter Piping System Friction A comprehensive chapter on pipe friction has been included in this Handbook for HVAC pumps because the sizing of pumps is determined... Electronics and HVAC Pumps How all these electronic procedures relate to HVAC pumps? Efficient pump selection and operation depend on the accurate calculation of a water system’s flow and pump head