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SHCS Calculator - Ver 1.2 Original spreadsheet edited for readability. VERSION HISTORY Basic Instructions: First and foremost, be sure to CLEAR any bold faced entries in the cells that don't apply to you (don't delete the cell contents! - select the cell to clear, then go to the "cells" menu and select "clear cells".) THEN follow these STEPS - STEP ONE - FILL IN THE YELLOW DATA CELLS - Calculate the Greenhouse Volume. We always start by calculating the total air volume of the greenhouse. If you know it already, there is a place to insert it. STEP TWO to STEP FIVE - FILL IN THE GREEN DATA CELLS for your fan, tubing and energy data - Read your results in the blue cells. STEP SIX - Share your numbers and discuss your options here. Enjoy! Remember, if you want to use your own SHCS Calculator for sharing or editing later, you must register as a user here. Then you can save a copy of this sheet for your own use. 1.0 - 2004, first stab at it, tubing air speeds and exchange rates guessed at from two of my prototypes, VERY CONSERVATIVE CHOICE OF AIR FLOWS AND FAN SIZES (Max exchange of 5 times per hour and Max tubing air speed of 4 feet per sec) DELETED from Numsum 1.1 - 2008, minor usability edits. Added comments to reflect that some field trials are changing the recommended air exchanges per hour and tubing air speeds. Larger energy transfers have been achieved using air flows 2-4 times my initial guesses. Details are here. Remember, we first calculate the volume of air in the greenhouse - fill in the YELLOW DATA cells in the Greenhouse Dimensions yellow section below. 1.2 -2009 Edited Calcs in Hoop Section Calculator, changed Width to Radius. After that, the next steps using the GREEN CELLS would start with selecting the number and size of the FANS to use to move all that air underground - Play around with the GREEN DATA CELLS to get close to the desired outcome in the BLUE CELLS "Exchange Rate" and "Tubing Air Speed". Don't forget, if you register as a Numsum user, you can save a copy of the SHCS Calculator for your personal use (analyze, export it to Excel format, study, tweek, and share online.) I would be happy to look at your numbers and make suggestions based on your figures. Join Numsum and create a copy for others to see! NOTE: Remember - your important Calculated figures are in cells this color for the entire sheet Field trial data will always change recommendations noted in this SHCS Calculator. Keep abreast of current known information here if you want the most current info I know about. DIRECT YOUR QUESTIONS SPECIFIC TO THIS SHEET'S TERMS AND METHODS TO THE SHCS FORUM. Ask any questions you have and get answers from me directly and from the rest of the community of solar greenhouse builders interested in the possibilities and opportunities - listen in (and register there if you want to add your voice or ask questions.) STEP ONE - Calculate the Greenhouse's Total Air Volume from it's Dimensions Just enter the Total Greenhouse Air Volume in Cell B20 if you already know it. The greenhouse "BOX" sections refers to the space that is defined by the straight up walls - the volume from the floor just to the top of the walls. Then you calculate and add in the volume of the roof section above the BOX sections, usually hoops... Use the Hoop Section's calculator if you have a hoop style curved roof (see NB#2 below). NB#1: a half circle hoop house has an 180 degree included arc. NB#2: This Hoop Section calculator applies only if the Diameter of the hoop's curve is the same as the width of the greenhouse. PS - it usually isn't! NB#3: If NB#2 does not apply, use this sheet to get a figure to use in CELL J18. NB#4: If you have a gabled or shed roof, you can just measure the height from the top of the walls to the top of the peak - fill in the respective Length and Width that apply and you will have the volume of your shed or gabled roof section included in the Total Greenhouse Volume. NOTE: IF NONE OF THESE VOLUME CALCS APPLY TO YOUR GREENHOUSE SHAPE, YOU CAN SIMPLY ENTER YOUR TOTAL VOLUME IN CELL B20 AND CLEAR ALL OF THE OTHER YELLOW CELLS. Box Sections Height Length Width Section Sub total CUFT Hoop Sections Arc Included Radius Length Hoop Section Sub Total CUFT Main 4 60 30 7200 Main 160 15 60 14075 Section2 0 0 0 Section2 Section3 0 0 0 0 Section3 Shed and Gable Roof Sections Height above Box Section Wall Length Width Main 0 0 0 Section2 0 0 0 Section3 0 0 0 Total Floor Space Square footage > 1800 Initial ballpark figure for total feet of 4" tubing for three layer concept design (about 1.33 feet per sqft of GH) > 2394 You can get more precise figures for your Hoop Section Volumes from here. Remember to zero out or clear the contents of Hoop Sections calculator cells above if you use the other calculator - place the figure you get in the cell just to the right of this one (just above the calculated value for "Total Hoop Volume CU/ft" - Cell J18 - make sure it's blank before you add the figure from the other calculator) Total GH Air Volume > 21587 Total Section CUFT > 7200 Total Hoop Section CU/FT 14075 If the calculator volume fails to work for your unique design, just enter your own total volume here (Cell B20) > 312 For every sq/ft of floor there is this many cu/ft of air : >> 11.992777777777778 Total wall area for Box and Shed Sections 720 Total roof area for Box and Shed Sections (approximate!) 1980.0000000000002 For every sq/ft of floor there is this much sq/ft of exposed wall and roof in the Box and Shed Sections (approximate!) >> 1.5 Now you decide how many and how big the FANS are going to be to move all the air in the greenhouse underground at least 5 times per hour when the sun is shining. Play with the Number of Fans in A26 and watch the BLUE cells C26, E26 and H30. Initial low end Design Numbers: at least 5 air exchanges per hour (filled in for you) and in cell H30, at least 2-4 feet per sec air speed in the Underground Air Circulation Tubing. These initial suggestions have been shown to provide at least 11 months of frost free Mediterranean climate in high altitude sunny Colorado AG Zone 4 with winterized solar heated greenhouses. Play around with the Number of Fans and the Fan CFM in cell D26 to get at least that outcome. Field trials indicate increasing energy transfers with increasing exchanges and air tubing speeds - up to 4 times more air exchanges has been trialed with favorable results. Keep abreast of the latest here. Don't change the italized BLUE Formula Cells!!! STEP TWO Fans Enter the number of fans you think might work. start with one per 2000 square foot of floor space (you can refer to the Floor Space figured for you in cell B18) . THEN, refering to the calculated CFM in cell C26, enter into cell D26 the CFM rating for the actual fan you have in mind or on hand (if you have the manufacturer's data sheet, use the CFM rating for 0.1" or 0.2" backpressure) Then play around, watching the blue cell E26 change... my Colorado experience suggested that at least 5 exchanges per hour was ideal. Current thought and recommendations from experience gained from more field trials have been noted here. Number of Fans Exchange Rate TIMES/HOUR you want in your design Fan CFM Calculated Fan CFM known or from Manufacturer's List Exchange Rate TIMES/HOUR Calculated for existing fan 2 5 899.4583333333334 900 5.003011071478204 A Standard underground tubing design uses buried 4" ADS tubing as a means to circulate the air of the greenhouse down through the soil. Three layers of 30' to 70' pieces are buried parallel to each other creating a tubing network under the entire floor area of the greenhouse. Tubing ends at one end of this network are plumbed together such that at least one fan per network can move greenhouse air down through all of the tubes equally. At the other end of the network, the tubing is identically plumbed together so that all the air returns back to the greenhouse. Enough tubing is included to provide effective heat exchange to and from the soil for at least 8 hours. That requires spacing the tubing such that there is at least 14" of soil between adjacent tubing walls with the upper wall of the top layer deep enough to avoid gardening damage from above. Check here for plumbing ideas for developing a design layout that works best for you. STEP THREE - Underground Air Circulation Tubing (UACT) B29/30 and C29/30 are standard for a 4" tubing system. Enter the tubing length - anything between 30 and 70 and the enter the number of tubes you need each fan to handle. Tubing Layout Designs originated here and are critiqued here. Then play around, watching the blue cells change. My Colorado prototypes suggested the "Tubing Air Speed" could be as low as 2 to 4 feet per second. Field trials noted here suggest air flows 2 to 4 times larger may be more effective. Number of Plenums (same as number of Fans) Tubing Diameter Effective Diameter Average Length of tubing # of tubes in each plenum Total Tubing Effective Area SQFT Total Feet of Tubing Tubing Air Speed FT/SEC Time in each Tube in SEC 2 4 3.75 57 21 3.2197265625 2394 9.317561419472247 6.11748046875 STEP FOUR - Cost of system hardware Enter the values that apply in the green cells. If you Repair, Re-use, Recycle, pretty much the only thing you need to buy is the tubing. Full blown tubing layouts cost me only $0.40 cents a sq ft, less than one season's fuel cost for Med Climate every year, all year from then on!! Per foot cost of your tubing in dollars (add $0.20 per foot if you need tubing with a sock soil filter) Total Tubing Cost Cost of each Fan & Plenum package (change to reflect your fan costs - plenums are $10-$15) Total Fan and Plenum cost Controls Package (only one required per greenhouse system) Total Hardware Costs 0.45 1077.3 100 200 100 1377.3 STEP Five - Payback Calculations Enter the correct rates for your situation in the green data cells. Enter the # of days you expect to get a 1 F deg Rise in the soil temperature. In Colorado, we get at least 180 days per year of full sunny gain sufficient to raise our soil mass temperature about one degree in a day. Your zone can be de-rated using Colorado as your reference. Florida and most of the SW are about the same solar incidence, the NE and NW may be as low as 100, the Mid States could be around 150. I'd like to put a calculated number here based on your Degree Day and Solar Exposure data, but that will have to be managed later... for now, we are stuck with a WAG solution (wild ass guess (:-) If you know an UNVENTED greenhouse in your area can get to 90 deg F for most of any one day, guess how many full days that might happen - that's the figure we are after. Mass of heatsink in pounds with soil mass at 80 lbs per cubic foot 432000 Heat stored with a 1 F deg rise in soil temp 432000 Your Therm cost ($ per 100,000 BTU's) go here for rates 1.55 Stored heat value as natural gas cost per 1 F deg rise 6.696000000000001 # of days you expect get a 1 F deg Rise in the soil temperature. 100 Gas Value gained each year 669.6 Your Electricity Cost in $/kilowatt hour (check here) 0.07 Annual Fan Operating cost (enter data below) 10.752 Yearly Net 658.8480000000001 Hardware Payback in Years 2.0904669969401133 Fan Power Calculation Volts Amps Wattage Daily Hours Number of fans (from A26) Total Daily KiloWatts Volts 120 .8 96 8 2 1.536
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