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Water-to-water heat pumps.

Many owners and designers of large commercial, institutional, and industrial (CII) facilities are considering the economic and environmental benefits of a water-to-water heat pump as a supplement to, or substitute for, a fossil fuel boiler. While a typical hot water boiler has a coefficient of performance (COP) of 0.85, heat pumps can have COPs of 3.50 or higher, which makes a compelling case for including heat pumps in many facilities.

An overview of the benefits and some of the applications for heat pumps appeared in an article titled "Using Waste Heat for Energy Savings," which was published in the April 2006 issue of ASHRAE Journal.

In CII facilities, a variety of water streams can act as heat sources for a heat pump. This article examines one application in detail: a facility that has a simultaneous requirement for chilled water and hot water, wherein the heat pump can provide or supplement both.

Facilities in which chilled water and hot water are often used simultaneously include: hospitals, pharmaceutical plants, hotels, and campus central utility plants. In these facilities, a heat pump can substantially cut energy consumption, and reduce a facility's carbon footprint.

This article discusses several system design guidelines, energy consumption calculations, green technology benefits, and capital constraint solutions for this specific heat pump application.

System Design Guidelines

These guidelines have been developed in conjunction with many facility owners and consulting engineers. They are general, rather than exhaustive, and focus on basic application questions, such as loads and hot water temperatures.

More detailed design guidelines, such as control systems and operation procedures, are the subject of a future article.

Load Profile. The ideal facility for this application would have a load profile similar to Figure 1, which illustrates a typical 24-hour day in each of the four seasons. The heat available from a heat pump (green line) is approximately 35% greater than the cooling load (blue line) because the heat of compression is included.

From Figure 1, it can be seen that during most of the operating season, the heat available in the chilled water loop is more than adequate to satisfy all or most of the hot water requirement (red line). Only during the periods represented by the patterned portion of the graph is the heat pump not able to produce 100% of the facility's hot water requirements. During these times, the heat pump can significantly supplement traditional sources of heat.

The heat pump should be the first heat source to be used, because it is most likely the low-cost heat source. That can be verified by the following calculations, which use energy costs of $0.068 per kWh of electricity and $11.21 per 1,000 [ft.sup.3] ($0.40 per [m.sup.3]) of natural gas:

Energy Cost of Natural Gas Boiler

100,000 Btu / 0.85 COP / 1,000 Btu/[ft.sup.3] x $11.21/1000 [ft.sup.3] = $1.32 per 100,000 Btu

(105,000 kJ / 0.85 COP / 37,500 kJ/[m.sup.3] x $0.40/[m.sup.3] = $1.32 per 105,000 kJ)

Energy Cost of Electric Water-to-Water Heat Pump

100,000 Btu / 3.83 COP / 3,415 Btu/kW x $0.068/kWh = $0.52 per 100,000 Btu

(105,000 kJ / 3.83 COP / 3600 kJ/kWh x $0.068/kWh = $0.52 per 105,000 kJ)

Location of Heat Pump. As illustrated in Figure 2, the most popular location for the heat pump is in a side-stream arrangement, between both water streams.

The heat pump is situated in this location for two reasons: 1) so it can be preferentially loaded before any of the chillers are brought on-line, and 2) so that the warmest return water is cooled in the heat pump, which slightly improves its COP.

Hot Water Temperature. One difference between the traditional boiler system and a heat pump system is that the hot water temperature supplied by the heat pump may be significantly lower. This is due to the necessity of balancing the economics of operating the heat pump, versus the capital and operating costs of the connected heating system.

Since the COP of a noncondensing boiler varies little over a large range of supply temperatures, traditional hot water heating designs standardized on a supply temperature of 180[degrees]F (82[degrees]C) with a rise of 30[degrees]F-40[degrees]F (17[degrees]C-22[degrees]C). This offered the benefit of low water flow rates, smaller piping, lower pumping costs, and less expensive heating coils.

[FIGURE 1 OMITTED]

On the other hand, the COP of a heat pump decreases significantly as the hot water supply temperature increases, as shown in Figure 3. Using the COP values in this graph can assist the system designer in selecting the optimum heating design temperature.

The COP values in Figure 3 are based on a chiller manufacturer's rating data for a heat pump system with a constant leaving chilled water temperature of 42[degrees]F (6[degrees]C), which is representative of many chilled water systems. For systems in which the leaving chilled water temperature is significantly different, heat pump manufacturers can supply revised data.

Specific utility rates, labor rates, system design, and material costs all contribute to the determination of the hot water supply temperature in a heat pump system. However, most system designers are finding that the optimum temperature is between 120[degrees]F and 150[degrees]F (49[degrees]C and 66[degrees]C).

Service Hot Water. Sometimes, the hot water temperature may be the minimum temperature required to ensure a bacteria-free service water supply. If the service hot water represents a relatively small percentage of the total hot water heating load, then consideration should be given to elevating the temperature of the service water with a separate fossil fuel or electric boiler.

Booster Heating. It is also possible that a specific heating system requirement, or an existing heating system design, may dictate a hot water supply temperature greater than the heat pump can supply. In that case, the heat pump condenser can be piped in series with a hot water boiler or steam converter, which can supply the final hot water temperature (Note: If this is done with a boiler, it is important to consult with the boiler manufacturer to ensure that the boiler can operate with a reduced hot water temperature difference and/or increased hot water flow rates).

In fact, effective operation of the heat pump dictates its capacity be less than the design chilled water and hot water loads. This is because any reduction of the cooling load handled by the heat pump will also reduce its heat output. So, it is desirable to keep the heat pump as close to fully loaded as possible. Therefore, one or more chillers, and one or more boilers, will be required to supplement the capacity of the heat pump.

[FIGURE 2 OMITTED]

Potable Water Isolation. Most building codes require two layers of separation between the oil and refrigerant in a heat pump condenser and any potable water supply. In that case, an isolation heat exchanger will be required. The additional heat transfer loss will slightly reduce the heat pump COP.

Energy Consumption Calculations

How much energy can a heat pump save in this type of application, and is it a good investment? An energy analysis of an actual facility demonstrates the economic potential of a heat pump. It also shows how these applications can be analyzed.

This analysis was recently performed for an Arizona hospital. It compares a conventional plant, which includes variable speed, centrifugal chillers and natural gas boilers, to an alternate plant that adds a heat pump to the conventional plant.

Several analysis methods are available. The two most popular are bin analysis and hour-by-hour analysis, and a close correlation has been found when both methods are used. For simplicity of presentation in this article, the bin method will be demonstrated.

Conventional System. The summertime design ambient temperatures are 120[degrees]F (49[degrees]C) dry bulb/72[degrees]F (22[degrees]C) wet bulb, and 27[degrees]F (-3[degrees]C) dry bulb/24[degrees]F (-4[degrees]C) wet bulb in the winter. The cooling towers produce 81[degrees]F (27[degrees]C) water in the summer, and are limited to 55[degrees]F (13[degrees]C) water in the winter. The design hot water load is 27,000 kBtu/h (7913 kW) and the efficiency of the boilers is 85%. A base hot water load of approximately 7,000 kBtu/h (2051 kW) exists at all times. The design cooling load is 4,200 tons (14 770 kW), and the variable speed chillers' efficiency values are drawn from the chiller ratings. The facility uses airside economizers below 55[degrees]F (13[degrees]C) dry-bulb ambient, but a base chilled water load of 400 tons (1,407 kW) exists at all times. Figure 4 shows the loads versus outdoor temperature.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The electrical rates from this particular utility vary by season and time-of-day, and these variations are approximated in the bin analysis varying the rates in each bin. For comparison purposes, the weighted average used in this analysis is $0.068/ kWh. The average natural gas rate used in the analysis is $11.21/ Mcf ($0.40/[m.sup.3]). Both rates are representative of rates found in North America.

The chillers and boilers will be analyzed separately and combined to establish a total cost. The analyses are shown in Tables 1 and 2 respectively.

The calculations used in Tables 1 and 2 (as well as Tables 3 through 5) are not complicated, but an explanation of the computations in one bin should ensure there is no confusion.

All weather data comes from Engineering Weather Data, which was complied by the Air Force Combat Climatology Center and was published in July 1978. Looking at the 120[degrees]F-115[degrees]F (49[degrees]C-46[degrees]C) bin in the chiller analysis, the Blue Book says that Phoenix spends an average of two hours per year in that temperature range, and that the mean coincident wet-bulb (MCWB) temperature is 72[degrees]F (22[degrees]C). Cooling tower ratings show that, under those conditions, the towers will supply 80.1[degrees]F (27[degrees]C) to the condensers of the chillers.

From Figure 4, the average chilled water load in this bin is 4,045 tons (14 226 kW) of refrigeration, and the chiller ratings peg their efficiency as 0.589 kW per ton at those conditions. The chiller power is a product of 4,045 tons x 0.589 [kW.sub.elec]/ [kW.sub.cool] = 2382 kW. During the two hours spent in this bin, the chiller energy consumption is two hours x 2,382 kW = 4,765 kWh.

The blended electrical use rate for this bin is $0.0734 per kWh, so the chiller operating cost is 4,765 kWh x $0.0734 per kWh = $350 annually. All the numbers in Tables 1 through 5 are calculated in a similar fashion.

Tables 1 and 2 contain the conventional system results, and show the annual operating cost as:

$472,402 (Chillers) + $1,156,894 (Boilers) = $1,629,296 (Total Annual Cooling and Heating Cost)

Alternate System. Next, a heat pump capable of 800 tons (2814 kW) of cooling and 13,500 MBH (3956 kW) of heating is added to the system. The heat pump is capable of handling almost the entire hot water load above 60[degrees]F (16[degrees]C) dry-bulb ambient. It is also capable of handling the entire cooling load below 55[degrees]F (13[degrees]C) dry-bulb ambient, but its cooling capability above 55[degrees]F (13[degrees]C) dry-bulb ambient is limited by how much hot water can be used productively. The analysis is shown in Tables 3, 4, and 5.

The summary of the annual operating cost for the heat pump plant is:

$380,659 (Chillers) + $252,043 (Boilers) + $417,049 (Heat Pump) = $1,049,751 (Total Annual Cooling and Heating Cost)

Therefore, adding the heat pump reduced the operating cost by: $1,629,296 - $1,049,751 = $579,545

The heat pump system, which had an additional capital cost of approximately $750,000, included the heat pump, piping, pumps, controls, and engineering design services. This investment resulted in a simple payback of 1.3 years, which is typical of the one- to two-year payback found in most hospital projects studied.

Energy Analysis Comments. This analysis does not include evaluation of the many ancillary devices (pumps, towers, etc.), which could be included in a detailed analysis. The energy consumption of these devices is relatively small compared to the major components presented here. In addition, many of these often offset each other and are not likely to significantly change by adding a heat pump to a system.

Electrical demand charges are a significant portion of most commercial electric utility bills, but they were not presented for simplicity. Adding a heat pump, which is expected to operate during even the hottest portions of the operating season, will increase the demand charges. However, because the heat pump's cooling capacity is displacing cooling that a chiller would normally contribute, only the net difference between the power of the heat pump and the equivalent power of a chiller must be added to calculate the additional demand charge for the heat pump. In most cases, the increase in demand charges is normally less than 5% of the total use costs and has a relatively minor effect on the total economic evaluation.

Green Technology Benefits

Reducing the consumption of fossil fuels to power HVAC equipment reduces the amount of C[O.sub.2] emitted to the atmosphere.

It is true that replacing a fossil fuel boiler with an electric drive heat pump causes the building electrical consumption to increase and this will increase C[O.sub.2] emissions at the utility power plant. However, this is more than offset by the significant reduction in C[O.sub.2] emissions by not burning as much fossil fuel to heat the building.

Also, if the facility owners and designers are interested in obtaining LEED[R] certification for the building, the addition of a heat pump can help. The U.S. Green Building Council's LEED rating system offers credits for exceeding the efficiency requirements of ASHRAE Standard 90.1. Substituting a heat pump for a hot water boiler helps to achieve this goal.

Capital Constraint Solutions

In spite of the tremendous economic and environmental benefits that heat pumps offer, designers may still find it difficult to incorporate a heat pump into an existing system, due to capital budget constraints. If the building owner is open to creative financing, then the additional equipment, facility, and design costs can be financed with future economic benefits.

In new facilities, another approach to reducing the capital outlay is to eliminate or reduce the size of the redundant chillers by taking advantage of the chilling capacity of the heat pump. The Arizona hospital example can be used to demonstrate this approach.

For this particular facility, the design loads are approximately 4,200 tons (14 770 kW) cooling and 27,000 kBtu/h (7913 kW) heating. Standard design practice for this critical-care facility dictates that a plant with multiple chillers be installed to meet the design load and provide redundant capacity in the unlikely event that one of the chillers is offline for maintenance or repairs during a peak-capacity period. The standard practice is to use an "N + 1" redundancy approach. The boiler system requires N + 1 redundancy for the same reasons.

For this facility, one option is to provide four 1,050 ton (3693 kW) chillers with a redundant 1,050 ton (3693 kW) chiller and two 13,500 kBtu/h (3957 kW) boilers with a redundant 13,500 kBtu/h (3957 kW) boiler. If the proposed 800 ton (2814 kW)/13,500 kBtu/h (3957 kW) heat pump is installed in lieu of the redundant chiller and boiler, and the four chillers are marginally increased in size to 1,133 ton (3985 kW) each, the full heating and cooling redundancy is maintained. The capital saved by not supplying either the redundant chiller or the redundant boiler can be used to offset the cost of the heat pump.

Conclusion

Water-to-water heat pumps have a COP of 3.50 or higher, while a typical hot water boiler has a COP of 0.85. That makes heat pumps worth investigating for many types of facilities. This article has examined some of the system design guidelines, energy consumption calculations, green technology benefits, and capital constraint solutions of a water-to-water heat pump applied in a facility that has simultaneous needs for chilled and hot water.

Given the many benefits that heat pumps offer, it is possible this technology will soon become a design standard in hospitals, pharmaceutical plants, hotels, and campus utility plants.

By Roy Hubbard, Member ASHRAE

Roy Hubbard is senior marketing manager, technology--HVAC systems, for the Building Efficiency business of Johnson Controls Inc., in York, Pa.
Table 1: Chiller analysis.

Bin Weather Data

      OADB             MCWB              ECWT           Bin
   ([degrees]F)     ([degrees]F)     ([degrees]F)      Hours

       117.5                72             80.1          2
       112.5                71             78.9         30
       107.5                71             78.6        184
       102.5                70             77.5        353
        97.5                69             76.3        473
        92.5                67             74.3        628
        87.5                65             72.3        680
        82.5                62             69.5        963
        77.5                59             66.6        827
        72.5                55             62.9        711
        67.5                52             59.5        638
        62.5                49             57.0        872
        57.5                47             55.0        791
        52.5                44             55.0        677
        47.5                41             55.0        486
        42.5                37             55.0        249
        37.5                33             55.0        165
        32.5                28             55.0         25
        27.5                24             55.0          6

Standard VSD Chiller Operating Cost

     Total              Chiller
  Chilled Water       Efficiency         Chiller
  Load (Tons)           (kW/Ton)       Power (kW)

       4,045             0.589            2,382
       3,864             0.583            2,253
       3,612             0.580            2,095
       3,538             0.579            2,048
       3,297             0.572            1,886
       3,009             0.499            1,502
       2,686             0.439            1,179
       2,457             0.380              934
       2,062             0.351              724
       1,745             0.277              483
       1,721             0.231              398
       1,721             0.227              391
       1,721             0.229              394
         400             0.229               92
         400             0.229               92
         400             0.229               92
         400             0.229               92
         400             0.229               92
         400             0.229               92

Standard VSD Chiller Operating Cost

                       Blended
      Chiller         Electrical         Chiller
       Energy          Use Rate         Operating
       (kWh)           ($/kWh)            Cost

       4,765             0.073            $350
      67,580             0.073          $4,960
     385,428             0.073         $28,290
     723,073             0.073         $53,074
     892,110             0.073         $65,481
     943,021             0.073         $69,218
     801,680             0.073         $58,843
     899,105             0.067         $59,790
     598,495             0.067         $39,800
     343,713             0.067         $22,857
     253,697             0.067         $16,871
     340,741             0.067         $22,659
     311,813             0.067         $20,736
      62,013             0.067          $4,124
      44,518             0.067          $2,960
      22,808             0.059          $1,337
      15,114             0.059            $866
       2,290             0.059            $134
         550             0.059             $32

Total Seasonal Chiller Operating Cost = $472,402

Table 2: Boiler analysis.

Bin Weather Data

            OADB                MCWB             ECWT
        ([degrees]F)        ([degrees]F)      ([degrees]F)    Bin Hours

            117.5                 72           80.1               2
            112.5                 71           78.9              30
            107.5                 71           78.6             184
            102.5                 70           77.5             353
             97.5                 69           76.3             473
             92.5                 67           74.3             628
             87.5                 65           72.3             680
             82.5                 62           69.5             963
             77.5                 59           66.6             827
             72.5                 55           62.9             711
             67.5                 52           59.5             638
             62.5                 49           57.0             872
             57.5                 47           55.0             791
             52.5                 44           55.0             677
             47.5                 41           55.0             486
             42.5                 37           55.0             249
             37.5                 33           55.0             165
             32.5                 28           55.0              25
             27.5                 24           55.0               6

Boiler Operating Cost

                        Heating Input to   Natural Gas    Natural Gas
  Hot Water Heating     85% Efficient      Consumption    Consumption
       Load (MBH)         Boiler (MBH)        (MBtu)         Cost ($)

            6,928              8,150         16,300             179
            6,894              8,110        243,313           2,676
            6,826              8,031      1,477,668          16,254
            6,836              8,042      2,838,890          31,228
            6,773              7,968      3,768,978          41,459
            6,681              7,860      4,936,189          54,298
            6,565              7,724      5,252,094          57,773
            6,497              7,644      7,361,210          80,973
            6,333              7,451      6,161,693          67,779
            7,341              8,636      6,140,161          67,542
            9,544             11,228      7,163,693          78,801
           11,757             13,832     12,061,629         132,678
           13,975             16,442     13,005,318         143,058
           16,193             19,051     12,897,586         141,873
           18,382             21,626     10,510,446         115,615
           20,538             24,162      6,016,329          66,180
           22,678             26,680      4,402,271          48,425
           24,780             29,153        728,835           8,017
           26,853             31,592        189,553           2,085

Total Season Boiler Operating Cost = $1,156,894

Table 3: Chiller analysis.

Bin Weather Data

      OADB              MCWB             ECWT              Bin
   ([degrees]F)     ([degrees]F)      ([degrees]F)        Hours

       117.5                72             80.1              2
       112.5                71             78.9             30
       107.5                71             78.6            184
       102.5                70             77.5            353
        97.5                69             76.3            473
        92.5                67             74.3            628
        87.5                65             72.3            680
        82.5                62             69.5            963
        77.5                59             66.6            827
        72.5                55             62.9            711
        67.5                52             59.5            638
        62.5                49             57.0            872
        57.5                47             55.0            791
        52.5                44             55.0            677
        47.5                41             55.0            486
        42.5                37             55.0            249
        37.5                33             55.0            165
        32.5                28             55.0             25
        27.5                24             55.0              6

Standard VSD Chiller Operating Cost

    Total                                  Net
    Chilled       Chiller/Heat        Conventional       Chiller
  Water Load      Pump Cooling       Chilled Water    Efficiency
    (Tons)       Capacity (Tons)       Load (Tons)      (kW/ton)

       4,045               412            3,633          0.589
       3,864               410            3,454          0.583
       3,612               406            3,206          0.580
       3,538               406            3,132          0.579
       3,297               403            2,894          0.572
       3,009               397            2,612          0.499
       2,686               390            2,296          0.439
       2,457               386            2,071          0.380
       2,062               376            1,686          0.351
       1,745               436            1,309          0.277
       1,721               567            1,154          0.231
       1,721               699            1,022          0.227
       1,721               800              921          0.229
         400               400               --          0.229
         400               400               --          0.229
         400               400               --          0.229
         400               400               --          0.229
         400               400               --          0.229
         400               400               --          0.229

Standard VSD Chiller Operating Cost

                                        Blended
     Chiller          Chiller         Electrical        Chiller
      Power            Energy          Use Rate        Operating
       (kW)            (kWh)            ($/kWh)          Cost

       2,140             4,280            0.073            314
       2,014            60,409            0.073          4,434
       1,859           342,100            0.073         25,110
       1,813           640,092            0.073         46,983
       1,656           783,076            0.073         57,478
       1,304           818,612            0.073         60,086
       1,008           685,257            0.073         50,298
         787           757,852            0.067         50,397
         592           489,351            0.067         32,542
         363           257,844            0.067         17,147
         267           170,133            0.067         11,314
         232           202,378            0.067         13,458
         211           166,902            0.067         11,099
           0                 0            0.067              0
           0                 0            0.067              0
           0                 0            0.059              0
           0                 0            0.059              0
           0                 0            0.059              0
           0                 0            0.059              0

Total Seasonal Chiller Operating Cost = $380,659

Table 4: Boiler analysis.

Bin Weather Data

          OADB              MCWB             ECWT            Bin
       ([degrees]F)      ([degrees]F)     ([degrees]F)      Hours

           117.5              72              80.1            2
           112.5              71              78.9           30
           107.5              71              78.6          184
           102.5              70              77.5          353
            97.5              69              76.3          473
            92.5              67              74.3          628
            87.5              65              72.3          680
            82.5              62              69.5          963
            77.5              59              66.6          827
            72.5              55              62.9          711
            67.5              52              59.5          638
            62.5              49              57.0          872
            57.5              47              55.0          791
            52.5              44              55.0          677
            47.5              41              55.0          486
            42.5              37              55.0          249
            37.5              33              55.0          165
            32.5              28              55.0           25
            27.5              24              55.0            6

Boiler Operating Cost

                       Chiller/Heat         Net Hot
      Hot Water        Pump Heating          Water
      Heating Load        Capacity          Heating
         (MBH)             (MBH)          Load (MBH)

           6,928           6,928                 0
           6,894           6,894                 0
           6,826           6,826                 0
           6,836           6,836                 0
           6,773           6,773                 0
           6,681           6,681                 0
           6,565           6,565                 0
           6,497           6,497                 0
           6,333           6,333                 0
           7,341           7,341                 0
           9,544           9,544                 0
          11,757          11,757                 0
          13,975          13,090               885
          16,193           6,690             9,503
          18,382           6,690            11,692
          20,538           6,690            13,848
          22,678           6,690            15,988
          24,780           6,690            18,090
          26,853           6,690            20,163

Boiler Operating Cost

          Heating
         Input to        Natural Gas      Natural Gas
      85% Efficient      Consumption      Consumption
       Boiler (MBH)         (MBtu)          Cost ($)

               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
               0               0               $0
           1,042         823,918           $9,063
          11,180       7,569,198          $83,261
          13,756       6,685,341          $73,539
          16,291       4,056,553          $44,622
          18,810       3,103,624          $34,140
          21,283         532,070           $5,853
          23,722         142,330           $1,566

Total Seasonal Boiler Operating Cost = $252,043

Table 5: Heat pump analysis.

Bin Weather Data

        OADB              MCWB            ECWT            Bin
    ([degrees]F)     ([degrees]F)    ([degrees]F)       Hours

         117.5              72             80.1            2
         112.5              71             78.9           30
         107.5              71             78.6          184
         102.5              70             77.5          353
          97.5              69             76.3          473
          92.5              67             74.3          628
          87.5              65             72.3          680
          82.5              62             69.5          963
          77.5              59             66.6          827
          72.5              55             62.9          711
          67.5              52             59.5          638
          62.5              49             57.0          872
          57.5              47             55.0          791
          52.5              44             55.0          677
          47.5              41             55.0          486
          42.5              37             55.0          249
          37.5              33             55.0          165
          32.5              28             55.0           25
          27.5              24             55.0            6

        Chiller/Heat Pump Operating Cost

                                        Chiller/
    Chiller/Heat       Chiller/        Heat Pump
     Pump Heating      Heat Pump       Electrical
    Capacity (MBH)     Power (kW)       Use (kWh)

         6,928             636            1,272
         6,894             634           19.015
         6,826             630          115,905
         6,836             630          222,559
         6,773             627          296,493
         6,681             622          390,306
         6,565             615          418,048
         6,497             611          588,250
         6,333             582          481,314
         7,341             677          481,347
         9,544             796          507,848
        11,757             968          844,096
        13,090           1,076          851,116
         6,690             580          392,660
         6,690             580          281,880
         6,690             580          144,420
         6,690             580           95,700
         6,690             580           14,500
         6,690             580            3,480

 Chiller/Heat Pump Operating Cost

                        Chiller/
       Blended         Heat Pump
    Electrical Use     Operating
    Rate ($/kWh)       Cost ($)

         0.073            $93
         0.073         $1,396
         0.073         $8,507
         0.073        $16,336
         0.073        $21,763
         0.073        $28,648
         0.073        $30,685
         0.067        $39,119
         0.067        $32,007
         0.067        $32,010
         0.067        $33,772
         0.067        $56,132
         0.067        $56,599
         0.067        $26,112
         0.067        $18,745
         0.059         $8,463
         0.059         $5,608
         0.059           $850
         0.059           $204

Total Seasonal Chiller/Heat Pump Operating Cost = $417,049
COPYRIGHT 2009 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2009 Gale, Cengage Learning. All rights reserved.

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Author:Hubbard, Roy
Publication:ASHRAE Journal
Geographic Code:1USA
Date:Jan 1, 2009
Words:4690
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