Instruction Guide: Residential Earth Loop Pressure Drop Calculation and Pump Sizing

Transcription

1 Instruction Guide: Residential Earth Loop Pressure Drop Calculation and Pump Sizing Table of Contents Preface Parallel vs. Series Piping Summary... 1 Closed Loop Sizing Summary Pressure Drop Calculation Instructions Residential Pressure Drop Calculation Worksheet...6 Other Pump Performance Curves Unit Pressure Drop Tables Pipe Pressure Drop Tables Equivalent Length of Fittings Fluid Performance Comparison Preface WaterFurnace s closed ground loop heat exchangers (GLHE) systems provide an excellent return on investment when properly installed. A site survey should be conducted to ensure that conditions are favorable for a closed loop installation. Some GLHE installation considerations are: Adequate space must be available for the GLHE installation. Earth conditions to four-six foot depth must be such that trenching can easily be done for horizontal installations. Soil type and moisture content must be favorable for efficient heat transfer. Horizontal closed loops must be properly backfilled to ensure good heat transfer. Trenches deeper than 5 feet must be shored for safety of personnel. On vertical earth loops a survey should be done to determine geological formation and estimated drilling costs. Vertical closed loops must be properly grouted, or sealed, to prevent cross contamination of aquifers and to ensure good heat transfer. NOTE: Horizontal earth loop backfilling tends to compact over a period of several months, and the performance improves as this compaction occurs. Parallel vs. Series Piping Parallel piping systems, when compared to series piping systems, provide these important features in GLHE systems: Low pressure drop, thus lower pumping costs Lower cost of pipe (generally) 3/4 IPS high density polyethylene is used for the circuits. This size is generally substantially less expensive than the larger pipe that would be required for a series loop of equal pressure drop. Good heat transfer vs. surface area It is for these reasons that WaterFurnace generally recommends parallel piping systems for GLHE systems where equipment tonnage exceeds 2 tons. Summary This manual is a guide to aid in calculating loop pressure drop and determining pump size(s) needed to deliver the best performance at the lowest power consumption. It should be noted, however, that a loop could be designed (which would be completely adequate from a thermal standpoint) that would function with a high pressure drop. However, this system would require a larger pump consuming higher pumping watts resulting in higher operating costs. This is not a recommended design. The pressure drop calculation method contained herein can be used on horizontal, vertical, pond/ lake, and horizontal/vertical hybrid loops for both series and parallel piping systems. 1

2 Figure 1: Vertical - Reverse Return 3 Ton Loop 4 Outside sypply and return 90 Elbow (Typical) Building Penetration - Watertight and Sealed Tee (Typical) 3 Inside Supply and Return 5 Circuit Piping (Runout Piping) Flow Center FCI Flow Center With 1 or 2 Pumps 6 Fittings Loop Out Loop In PVC Pipe Inside Outside Wall Recommended Building Penetration PE Pipe Unit 1 Hose Kit or Inside Piping 1 Fernco Rubber Adaptor Wall Inside Closed Loop Sizing Summary A) One ton of heating / cooling = 12,000 BTU. (One BTU is the amount of heat required to raise one pound of water 1 degree Fahrenheit). B) 3 gpm per ton of WFI equipment recommended flow rate for closed loops, 2.25 gpm per ton minimum flow rate for closed loops. C) 1 circuit per ton (with pressure drop exceptions) D) Total gpm = Flow through each circuit Number of Circuits E) 2 feet of head for each 10 fittings (up to 7 tons) - Over 7 tons, calculate the equivalent pipe lengths and add to sup ply/return and circuit piping. F) A pressure drop calculation must be performed to determine the number of pumps. G) All circuits should be equal in length (maximum 10% difference) and manifold headers should be piped in reverse return to ensure equal flow through circuits. Multiple units can be supplied using one pumping system if the total flow rate and the total system pressure drop can be met by the pump(s). Calculate ALL WaterFurnace unit heat exchanger pressure drops (resistance to flow) at their respective flow rates (they should be piped in parallel single molecule of water will only flow through one of them). Flow rate for units piped in parallel should be added together while resistance to flow/pressure drop that the pump is working to overcome is the unit with the largest pressure drop. 2

3 Pressure Drop Calculation Instructions 1) Fill in ALL BLANKS in information block at top of Pressure Drop Calculation Worksheet. Job/Client Name GSC Technician Loop Description Total Trench/Bore Number of Circuits Antifreeze Minimum Loop Temperature 2) Unit Pressure Drop A) Enter unit model number in 1a. B) Find unit on Residential Unit Pressure Drop Tables. Model Number NS030 NS036 Pressure Drop Correction Factor Flow Rate (gpm) EWT (Deg F) Factor Pressure Drop (ft. of hd.) Pressure Drop (psi) st column for open loop (1.5 gpm/ton if EWT > 50 F; 2 gpm/ton if EWT < 50 F) 2 nd column minimum for closed loop (2.25 gpm/ton) Multiply this factor times the unit pressure drop if not at 50 F (10 C) 3 rd column Recommended for closed loop (3 gpm/ton) C) Enter Flow rate (gpm), and Pressure Drop (feet of head) from closed loop (optimum) column (recommended flow rate for closed loop, 3 gpm/ton). D) Enter Pressure Drop Correction Factor for proper entering water temperature (use 30 F for closed loops), and multiply by feet of head for that unit. Enter this number at far right, this is the feet of head for Unit #1, without rubber hose. a. WF Unit gpm ft. of hd. x temp. corr. factor = ft. of hd. 1 b. Hose gpm ft. x ft. of hd./100 ft. = ft. of hd. c. Inside gpm ft. x ft. of hd./100 ft. = ft. of hd. (Flow Center to Unit) Pipe Size TOTAL Unit #1 a. WF Unit gpm ft. of hd. x temp. corr. factor = ft. of hd. b. Hose gpm ft. x ft. of hd./100 ft. = ft. of hd. 2 c. Inside gpm ft. x ft. of hd./100 ft. = ft. of hd. (Flow Center to Unit) Pipe Size TOTAL Unit #2 ft. of hd. Unit TOTAL (Largest of Total Unit #1 and Unit #2) ft. of hd. 3

4 Pressure Drop Calculation Instructions cont. 3) Rubber Hose Pressure Drop A) Use 1 Rubber Hose Chart for equivalent pipe size. B) Enter total system gpm. C) Enter total feet in rubber hose. Rubber hose has high resistance to flow, maximum length 10 on supply and 10 on return, total maximum is 20. D) Enter feet of head/100 feet from chart in this manual. E) Divide total feet of rubber hose by 100, then multiply that number by feet of head/100 feet. Enter this number at far right. This is feet of head for rubber hose. F) Add the feet of head of the unit to the feet of head of the rubber hose. This is the Total Unit #1 feet of head. a. WF Unit gpm ft. of hd. x temp. corr. factor = ft. of hd. 1 b. Hose gpm ft. x ft. of hd./100 ft. = ft. of hd. c. Inside gpm ft. x ft. of hd./100 ft. = ft. of hd. (Flow Center to Unit) Pipe Size TOTAL Unit #1 4) Inside Supply and Return Pressure Drop A) Enter size of piping. B) Enter total system gpm (Total of the gpm required by each unit). C) Enter total footage inside supply and return (wall penetration to flow center pump(s), both directions). D) Enter feet of head/100 feet from chart in this manual. E) Divide total footage by 100, then multiply that number by feet of head/100 feet. Enter this number at far right. This is the feet of head" for the inside supply and return. (If total footage = 100 feet, multiply feet of head/100 feet by 1. If the total footage = 230 feet, multiply feet of head/100 feet by 2.3.) 3 Inside Supply Return Piping(to gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size 5) Outside Supply and Return Pressure Drop A) Enter size of piping. B) Enter total system gpm (Total of the gpm required by each unit). C) Enter total footage of outside supply and return (wall penetration to manifold, both directions). D) Enter feet of head/100 feet from chart in this manual. E) Divide total footage by 100, then multiply that number by feet of head/100 feet. Enter this number at far right. This is the feet of head for the outside supply and return. (If total footage = 100 feet, multiply feet of head/100 feet by 1. If total footage = 230 feet, multiply feet of head/100 feet by 2.3.) 4 Outside Supply & Return gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size 4

5 Pressure Drop Calculation Instructions cont. 6) Circuit Piping Pressure Drop A) Enter size of piping. B) Enter circuit gpm (divide total gpm by number of circuits to get circuit gpm). C) Enter total circuit length (if circuit is one 200 deep bore, circuit is 400 ; if circuit is one leg of a 6-pipe loop in a 400 long ditch, circuit is 800 ). D) Enter feet of head/100 feet from chart in this manual. E) Divide circuit length by 100, then multiply that number by feet of head/100 feet. Enter this number at the far right. This is the feet of head for the Circuit Piping. (If total footage = 100 feet, multiply feet of head/100 feet by 1. If total footage = 230 feet, multiply feet of head/100 feet by 2.3.) F) Check Reynolds number for circuit piping at circuit gpm from pipe pressure drop charts. Reynolds number must exceed Circuit gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size 7) Fittings For a typical residential job, up to 7 tons, add 2 feet of head for every 10 fittings. If more than 7 tons, count the number of fittings and convert into an equivalent pipe length from page 16 of this manual. Then figure the pressure drop using steps from the SUPPLY and RETURN pressure drop section. 6 Fittings (Add 2 ft. of hd. for every 10 fittings) ft. of hd. 8) Total System Pressure Drop A) Take gpm from the unit section and enter in Total gpm. B) Add up feet of head from each section and enter this number in the Total pd. TOTAL SYSTEM PRESSURE DROP Total gpm= Total pressure drop= ft. of hd. 9) Plotting Piping System Curve A) Use Total gpm and Total pd for Point 1. B) For Point 2; multiply Total gpm by.667, and multiply Total pd by.5. C) For Point 3; multiply Total gpm by 1.33, and multiply Total pd by 2. D) Plot these three points on the Piping System Curve / Pump Curve chart using feet of head and GPM. E) Starting at 0 gpm and 0 feet of head, draw a curving line through points 1, 2, and 3. F) Find the spot where this curved line crosses the pump curves and draw a line straight down to the gpm line at the bottom of the chart. This will determine if you need one or two pumps. 5

6 Residential Pressure Drop Calculation Worksheet Job/Client Name GSC Technician Loop Description Total Trench/Bore Number of Circuits Antifreeze Minimum Loop Temperature a. WF Unit gpm ft. of hd. x temp. corr. factor = ft. of hd. 1 b. Hose gpm ft. x ft. of hd./100 ft. = ft. of hd. c. Inside gpm ft. x ft. of hd./100 ft. = ft. of hd. (Flow Center to Unit) Pipe Size TOTAL Unit #1 a. WF Unit gpm ft. of hd. x temp. corr. factor = ft. of hd. b. Hose gpm ft. x ft. of hd./100 ft. = ft. of hd. 2 c. Inside gpm ft. x ft. of hd./100 ft. = ft. of hd. (Flow Center to Unit) Pipe Size TOTAL Unit #2 ft. of hd. Unit TOTAL (Largest of Total Unit #1 and Unit #2) ft. of hd Inside Supply Return Piping(to gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size Outside Supply & Return gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size Circuit gpm ft. x ft. of hd./100 ft. = ft. of hd. Pipe Size 6 Fittings (Add 2 ft. of hd. for every 10 fittings) ft. of hd. TOTAL SYSTEM PRESSURE DROP Total gpm= Total pressure drop= ft. of hd. The purpose of the following formulas is to generate 3 points on the system performance curve. Point 1 Total gpm = 3 gpm per ton = Total pd = pd of the system = Point 2 Total gpm 2 =.667 x gpm = Total pd 2 =.5 x pd = Point 3 Total gpm 3 = 1.33 x gpm = Total pd 3 = 2 x pd = Grundfos Pump Curve - UP26-99 HEAD (FEET) UP26-99 SINGLE UP26-99 DOUBLE Point 1 is generated from the design flow need and the pressure drop (pd) associated with this particular piping system. Points 2 and 3 are generated from point FLOW (GPM) NOTE: If using pumps other than shown, refer to the manufacturer s performance data. for those pumps 6

7 Other Pump Performance Curves Flow Center - 3 Pumps 100 Typical Large System Pump Curves FC3 60 Pressure Drop (FT HD) Pressure Drop (ft hd) Gallons per Minute Flow (gpm) Residential Unit Pressure Drop Tables Series Envision Single Speed Envision Dual Capacity E & EZ Single Speed E & EZ Dual Capacity Closed Loop (minimum) Closed Loop (optimum) Model & Size Flow Rate Pressure Drop* Flow Rate Pressure Drop* GPM PSI Ft. Head GPM PSI Ft. Head NS NS NS NS NS NS NS ND026 Low ND026 High ND038 Low ND038 High ND049 Low ND049 High ND064 Low ND064 High ND072 Low ND072 High E E E E E E E E036 Low E036 High E048 Low E048 High E060 Low E060 High E072 Low E072 High * Pressure Drops shown at 50 F EWT. For Pressure Drops at other EWTs, use table below. Ent. Water Temp. F C Correction Factor

8 Residential Unit Pressure Drop Tables cont. Series ES Single Speed ES Dual Capacity Synergy3D Synergy3 Legend Versatec Ultra Premier Closed Loop (minimum) Closed Loop (optimum) Model & Size Flow Rate Pressure Drop* Flow Rate Pressure Drop* GPM PSI Ft. Head GPM PSI Ft. Head ES ES ES036 Low ES036 High ES048 Low ES048 High ES060 Low ES060 High ES072 Low ES072 High SDV038 Low SDV038 High SDV049 Low SDV049 High SDV064 Low SDV064 High SDV072 Low SDV072 High RT RT RT LS LS LS LS LS LS LS US US US US US US US US US US US US US P P P P P P P P P P

9 Residential Unit Pressure Drop Tables cont. V(L/X) V(L/X) V(L/X) V(L/X) Versatec V(L/X) Vertical V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) Versatec V(L/X) Horizontal V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) V(L/X) NSW018R NSW018H NSW025R Envision NSW025H NSW Hydronic NSW040H/R NSW050H/R NSW060H/R NSW075H/R NDW Envision NDW NDW Hydronic NDW NDW EW EW EW Water-to-Water EW EW Premier P Water-to-water P Versatec V036W Water-to-water V060W C C Console C C C

10 Pipe Pressure Drop Tables Pressure Drop for Rubber Hose Per 100 ft, of hose, in feet of head BRINE 1 32 F BRINE 4 20% 30 F Viscosity lbm/ft sec Darcy-Weisbach Method Viscosity lbm/ft sec Darcy-Weisbach Method Density lb/ft3 Density lb/ft3 FLOW 1 IPS RUBBER HOSE 1 1/2 IPS RUBBER HOSE FLOW 1 IPS RUBBER HOSE 1 1/2 IPS RUBBER HOSE RATE PD (ft) Re PD (ft) Re RATE PD (ft) Re PD (ft) Re Rev. 1/06 Rev. 1/06 BRINE 8 25% 30 F BRINE 5 30% PROPYLENE 30 F Viscosity lbm/ft sec Darcy-Weisbach Method Viscosity lbm/ft sec Darcy-Weisbach Method Density lb/ft3 Density lb/ft3 FLOW 1 IPS RUBBER HOSE 1 1/2 IPS RUBBER HOSE FLOW 1 IPS RUBBER HOSE 1 1/2 IPS RUBBER HOSE RATE PD (ft) Re PD (ft) Re RATE PD (ft) Re PD (ft) Re Rev. 1/06 Rev. 1/06 10

11 Pipe Pressure Drop Tables cont. Pressure Drop, Polyethylene Pipe, SDR 11 Per 100 ft. of pipe, in feet of head BRINE 1 32 F Viscosity lbm/ft sec Density lb/ft3 Darcy-Weisbach Method FLOW RATE 3/4 IPS SDR 11 1 IPS SDR /4 IPS SDR /2 IPS SDR 11 2 IPS SDR 11 PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re Rev. 1/06 11

12 Pipe Pressure Drop Tables cont. BRINE 2 Viscosity F lbm/ft sec Density lb/ft3 Darcy-Weisbach Method 3/4 IPS SDR 11 1 IPS SDR /4 IPS SDR /2 IPS SDR 11 2 IPS SDR 11 FLOW RATE PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re Rev. 1/06 12

13 Pipe Pressure Drop Tables cont. Pressure Drop, Polyethylene Pipe, SDR11 Per 100 ft. of pipe, in feet of head 25% BRINE 8 30 F Viscosity lbm/ft sec Density lb/ft3 FLOW RATE Darcy-Weisbach Method 3/4 IPS SDR 11 1 IPS SDR /4 IPS SDR /2 IPS SDR 11 2 IPS SDR 11 PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re Rev. 1/6/06 13

14 Pipe Pressure Drop Tables cont. 20% BRINE 4 30 F Viscosity lbm/ft sec Density lb/ft3 FLOW RATE Darcy-Weisbach Method 3/4 IPS SDR 11 1 IPS SDR /4 IPS SDR /2 IPS SDR 11 2 IPS SDR 11 PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re Rev. 1/6/06 14

15 Pipe Pressure Drop Tables cont. Pressure Drop, Polyethylene Pipe, SDR 11 Per 100 ft. of pipe, in feet of head BRINE 5 30% PROPYLENE 30 F Viscosity lbm/ft sec Density lb/ft3 Darcy-Weisbach Method 3/4 IPS SDR 11 1 IPS SDR /4 IPS SDR /2 IPS SDR 11 2 IPS SDR 11 FLOW RATE PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re PD (ft) Re Rev. 1/06 15

16 Equivalent Length of Fittings Figure 2: Pressure Drop Through Tees A B A has pressure drop of a coupling. Tee Branch B has the pressure drop of a tee branch. Since B is a 1.5 x 1.5 x 1 tee, use the chart below for the equivalent length of pipe. Example: If B is a 2 x 2 x 1.25 tee, the resistance to flow through the tee-brach portion of the fitting is equal to 7 feet of 1.25 pipe. Question: If B is a 1.25 x 1.25 x.75 tee, the resistance to flow through the tee-brach portion of the fitting is equal to feet of pipe. Fitting Size.75" 1" 1.25" 1.5" 2" Coupling Elbow, 45 degree Elbow, 90 degree Tee-branch Fluid Performance Comparison Brine Solution Type Reynolds Number* (Turbulence) Feet of Head per 100' of Pipe (Resistance to Flow).75" pipe 1" pipe.75" pipe 1" pipe 32 F F % 30 F F (ethanol ) % Propylene 30 F 19% Propylene 30 F NOTE: All data at 3 gpm. *A minimum Reynolds Number of 2500 is required for all circuit piping WaterFurnace International, Inc., 9000 Conservation Way, Fort Wayne, IN WaterFurnace has a policy of continual product research and development and reserves the right to change design and specifications without notice. 16