June 2004: the load analyzer's next step? Sensible formulas

Engineered Systems, August, 2004 by Michael Kjelgaard

Although not a budget buster, the data shows that June '04 likely caused higher than normal cooling costs in southern cities and up the east coast as far as New York. The impact of weather on cooling costs in cities north of New York seemed to be typical, or sometimes below normal for June. Moving inland towards the Midwest, cooling degree days and VLI data were below normal as well. Also, the dry bulb temperature in most cities never reached the normal maximum or the normal minimum. As a result, June could be considered to be a pretty uneventful (but comfortable) month for most cities, since the high and low extremes were avoided. The data also shows that for most cities, there were very few ASHRAE cooling or wet bulb design hours, leaving the cooling equipment untested so far this year.

BIN DATA TOOLS: BUILDING THE VENTILATION ANALYZER (PART 4)

This is the fourth in a series of columns constructing a ventilation load analyzer that is capable of calculating ventilation and humidification costs and evaluating cooling coil condensate flow. To summarize where we are to date, we started by creating the VLABin.xls in a file in Microsoft Excel. We obtained the sample 5[degrees]F dry bulb and 5-grain humidity ratio bin data text files online from the website. We created a worksheet within VLABin.xls called "Sensible" and inserted the dry bulb bin data into it. Similarly, we inserted the humidity ratio bin data into a separate worksheet called "Latent." Last month, we created a third worksheet called "Input" and entered the sample input data. The next step is to enter the formulas that will be used into the sensible and talent worksheets.

STEP 3: ENTERING THE FORMULAS

Enter the Figure 3A formulas into the "Sensible" worksheet as shown in Figure 3. Columns A through E are data inserted from the dry bulb bin data file. Enter the formulas into the third row of columns F through K and copy them down to the bottom row of the bin data file (row 27 in this case). In the 28th row, enter the sum total formulas as shown. Follow the same steps in rows 3 through 20 of the latent worksheet (Figure 4) using the formulas in Figure 4A. Your results should match the results in Figures 3 and 4. If not, check to make sure you didn't overwrite the bin data when you copied the formulas down. Note that when you insert bin data from another city, there will likely he a different total number of bin data rows compared to the Cut Bank, MT data. You just need to make sure that the sum total row includes all of the data and that the proper ceils are referenced when evaluating the output.

The sensible and latent formulas simulate a 100% outside air system with heating, cooling, and humidification capabilities. Sensible heating and cooling is calculated from the difference between the bin average temperature and the desired temperature leaving the unit (55[degrees] in this example). Latent cooling, or dehumidification, is based on the bin average humidity ratio and the humidity ratio associated with the leaving air temperature at saturation (55[degrees] db / 100% rh). The humidification load is based on the bin average humidity ratio and the calculated humidity ratio associated with the desired space relative humidity (30% rh at 70[degrees] space in this case).

Note that the dry bulb and humidity ratio bin data files used in this spreadsheet tool are based on the calculated average value of each bin and not on the commonly used midrange value of the bin. In other words, if you look at the first humidity ratio bin in the latent worksheet, the bin value is 3.94 grains instead of 2.5 grains, which would be the midrange of the 0 to 5 grain bin. Using the bin average value instead of the midrange provides for much better accuracy, as we will show in next month's column when we evaluate the results.

FIGURE 1.

                        Degree Days
                     (Base 65[degrees]F       Dry Bulb Temperature

   June 04       HDD     N     CDD     N     Max     N     Min     N
                                            Deg F         Deg F

Atlanta           0      1     336    354    92     94     61     57
Baltimore        13     10     197    243    91     95     53     49
Boston           56     48     95     143    92     93     49     50
Chicago          44     48     108    160    90     93     47     43
Cleveland        53     50     107    152    90     92     46     43
Dallas            0      0     430    492    93     99     66     60
Denver           101    55     68     131    96     95     41     42
Detroit          36     46     96     140    90     92     47     44
Houston           0      0     486    485    95     97     68     62
Los Angeles       1     22     51     52     74     82     58     55
Memphis           0      0     410    425    93     96     63     58
Miami             0      0     572    500    92     93     73     70
Minneapolis      62     47     69     146    95     93     47     44
New York City    13     13     229    222    94     93     56     52
Philadelphia     13     11     213    232    92     94     56     50
Phoenix           0      0     783    688    109    112    71     62
Salt Lake City   18     52     185    167    93     98     48     42
San Diego         0     12     84     66     74     82     61     57
San Francisco    108    125     2     19     80     88     51     48
St. Louis         0      6     280    321    92     96     56     52
Seattle          105    152    51     21     88     85     47     45
Washington, DC    4      4     252    301    91     95     57     54

                  Wet Bulb     Hum. Ratio     Enthalpy     Dew Point
                   Deg F      Grains / Lb     Btu / Lb       Deg F

   June 04       Max    Min    Max    Min    Max    Min    Max    Min

Atlanta          78     58    140.9  61.7   41.8   25.5    76     53
Baltimore        77     51    135.7  39.9   40.2   20.7    76     42
Boston           75     46    102.9  25.5   38.0   18.2    68     31
Chicago          76     44    120.3  24.8   39.4   17.1    72     30
Cleveland        77     46    130.6  38.9   40.7   18.0    74     41
Dallas           78     63    130.1  76.4   41.5   28.8    74     59
Denver           64     38    94.8   21.2   31.2   15.2    60     22
Detroit          77     44    126.3  34.4   40.8   17.3    73     38
Houston          81     65    151.6  89.5   44.4   30.3    79     64
Los Angeles      68     54    100.3  54.3   32.7   22.7    67     50
Memphis          79     58    133.0  47.6   41.6   25.4    75     47
Miami            81     70    156.3  92.4   44.4   33.5    80     65
Minneapolis      76     45    114.0  30.9   39.7   17.6    70     35
New York City    78     51    135.8  28.2   41.0   20.3    76     34
Philadelphia     77     51    127.6  36.0   40.4   20.6    74     40
Phoenix          67     51    57.7   11.8   31.0   21.0    51     14
Salt Lake City   62     45    84.3   23.6   29.5   18.3    58     26
San Diego        65     56    80.6   49.4   29.9   23.5    61     48
San Francisco    64     49    77.8   46.0   29.3   19.9    60     46
St. Louis        80     53    149.4  47.2   44.1   22.3    78     46
Seattle          65     46    76.4   30.2   29.5   18.2    59     35
Washington, DC   79     51    135.7  40.5   42.0   20.8    76     43

                    ASHRAE Design Hrs

                  Cooling      Wet Bulb

   June 04      0.4%   1.0%   0.4%   1.0%

Atlanta           0      1      1      7
Baltimore         0      0      0      8
Boston            3     13      0      3
Chicago           0      6      0      4
Cleveland         2      8      5     17
Dallas            0      0      0      7
Denver            6     12      0      4
Detroit           0      7      3     14
Houston           0      2      3     18
Los Angeles       0      0      0      0
Memphis           0      0      0      0
Miami             3     22      4     20
Minneapolis       7      9      0      9
New York City     5     14      6     11
Philadelphia      0      4      0      0
Phoenix           0      1      0      0
Salt Lake City    0      0      0      0
San Diego         0      0      0      0
San Francisco     0      2      0      4
St. Louis         0      0      9     16
Seattle           6     32      0      0
Washington, DC    0      0      0      2

Figure 2.

June '04 Total Cooling VLI (Ton-hrs / CFM)

         ATL    BAL    BOS    CHI    CLE    DAL    DEN

Jun-04   2.76   1.83   0.98   1.27   1.30   3.15   0.50
Jun-03   2.46   1.70   1.19   0.94   1.21   3.15   0.50
Jun-02   2.58   2.39   1.06   1.78   1.75   3.23   1.10
Normal   2.17   1.97   1.07   1.43   1.55   2.90   0.71

         DET    HOU     LA    MEM    MIA    MIN    NYC

Jun-04   1.20   3.85   1.08   2.93   4.18   0.86   1.65
Jun-03   1.10   4.11   0.87   2.45   4.36   1.14   1.44
Jun-02   1.62   3.92   0.95   3.14   4.07   1.85   1.74
Normal   1.32   3.52   0.79   2.99   3.74   1.38   1.42

         PHIL   PHX    SLC     SD     SF    STL    SEA     DC

Jun-04   1.76   2.19   0.88   0.94   0.36   2.37   0.53   2.05
Jun-03   1.98   2.43   1.11   0.78   0.42   1.78   0.53   1.87
Jun-02   1.97   2.55   1.21   0.78   0.33   2.78   0.45   2.23
Normal   1.70   2.29   0.86   1.06   0.29   2.63   0.36   1.82

FIGURE 3. Sensible calculation worksheet.

        A          B          C           D          E

1   CUT_BANK MT 2003
2      >=          <        Hours     Dry Bulb   Hum. Rat.
3      -25        -20         3        -22.33       1.37
4      -20        -15         1          -17        1.93
5      -15        -10         3        -12.67       2.44
--     --         --          --         --          --
--     --         --          --         --          --
27     95         100         7         96.29      45.56
28
        F          G          H           I          J           K

1   Abs Temp      AD       CLG Sen     CLG Sen    HTG Sen     HTG Sen
2     T(R)       #/FT3       Btu       Ton-hr       Btu       Therms
3    437.34      0.079        0          --       26357730      264
4    442.67      0.078        0          --       8081842       81
5      447       0.077        0          --       22566689      226
--     --         --          --         --          --         --
--     --         --          --         --          --         --
27   555.96      0.062     25831958     2,153        0          --
28              Totals    1809532717   150,794   5398587554   53,986

FIGURE 3A. Spreadsheet worksheet formulas.

Cell       Formula

F3         =D3 459.67

G3         =Input!$B$7*144/F3/53.3

H3         =IF(D3>Input!$B$ll,Input!$B$29*C3*(D3-
           Input!$BS11)*0.24*60*G3,0)

I3         =H3/12000

J3         =IF(D3Input!$B$13,Input!$B$29*C3*(E3-
           Input!$B$13)*60*G3/7000,0)

I3         =H3*1050/12000

J3         =IF(E3=          <        Hours     Dry Bulb   Hum. Rat.
3       0          5          91        -3.18       3.94
4       5         10         245        9.04        7.47
5      10         15         381        24.51      12.82
--     --         --          --         --          --
--     --         --          --         --          --
19     80         85          1          58        80.36
20

        F          G          H           I          J           K

1   Abs Temp      AD       CLG Lat     CLG Lat    HTG Lat     HTG Lat
2     T(R)       #/FT3     Lbs Wtr     Ton-hr     Lbs Wtr     Therms
3    456.49      0.076        0          --        197699      2,076
4    468.71      0.074        0          --        463817      4,870
5    484.18      0.071        0          --        573722      6,024
--     --         --          --         --          --         --
--     --         --          --         --          --         --
19   517.67      0.067       350         31          0          --
20              Totals       635         56       2568892     26,973