Radiant Based HVAC Systems
Differential Pressure
Fundamentals of Hydronic Design This educational material is copy written by Robert Bean, R.E.T., All Rights Reserved. If you wish to use this presentation for non commercial or for profit purposes, please contact info@healthyheating.com for details and restrictions. Portions of this presentation are copy written by others including materials copy written 2005, by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted with permission from ASHRAE Applications Handbook. This material may not be copied nor distributed in either paper or digital form without permission. Some slides contained animations in the original.ppt format which have been eliminated in the conversions to Adobe s.pdf format.
Fundamentals of Hydronic Design Differential Pressure Is required to maintain design flow across: The System Pipe, Fittings, Service and Control Valves Heat Terminal Units Boilers, Chillers, Tanks, Heat Exchangers
Fundamentals of Hydronic Design Differential Pressure p = 0
Fundamentals of Hydronic Design Differential Pressure p = +
Fundamentals of Hydronic Design Differential Pressure p
Differential Pressure p Goal: Accumulated inventory of all the head losses in the piping network which the circulator must overcome. WinCAPS demo
Fundamentals of Hydronic Design Differential Pressure Example: Calculate the head losses in a 500,000 Btu/hr snow melt. Q w, Heat Transfer, Btu/hr 60 min/hr * p w lbs/usgal * c p Btu/lb o F * t o F 500,000 Btu/hr 60 min/hr * 8.76 lbs/usgal * 0.86 Btu/lb o F * 30 o F = q w, USgpm = 33 USgpm 100 o F 33 US gpm 130 o F Average = 115 o F
Differential Pressure Flow, q w = 33 USgpm Distribution Pipe & Fittings Snowmelt Manifold Snowmelt Pipe, 25 loops p Sub System
Differential Pressure - Pipe Flow, q w = 33 USgpm Distribution Pipe & Fittings ask what diameter of copper pipe for velocity between 1.5 and 5 fps and 1 to 4 ft of head/100 ft of pipe? See next page?
30 20 Pipe Diameters, Inches 3 FPS 4 FPS 3/8 ½ 5/8 ¾ 1 1-1/4 1-1/2 2 2-1/2 3 4 5 6 6 FPS 8 FPS 10 FPS 15 FPS 2 FPS Head Loss, ft / 100 ft 10 8 6 4 3 2 1 1.5 FPS 1 FPS K M 0.5 0.2 1 2 3 4 5 810 20 30 40 60 80 100 200 300 600 1000 400 800 2000 3000 Volumetric Flow Rate, USgpm System Syzer demo
Differential Pressure Pipe (less tube) Flow, q w = 33 USgpm 2 Copper 3.5 fps 2.5 ft / 100 ft p Pipe =.45 ft Head Loss in Distribution Pipe 18 of 2 Copper (18 /100 ) x 2.5 = 0.45 ft of head 5 5 2 2 2 2
Differential Pressure Fittings (less manifold) Flow, q w = 33 USgpm 2 Copper Fittings 4 Elbows 2 Pump Adapters 2 Manifold Adapters p Fittings??
Differential Pressure - Fittings Valves & Fitting Head Losses Choose either a) Percentage of Pipe Length Method ( do not include radiant pipe) 50% to 100% Allowance based on straight lengths of pipe. For basic piping systems Straight lengths x 50% = length of pipe allowed for fittings For complex piping systems Use 75% to 100% b) Fitting Equivalent Method Detailed procedure requiring complete inventory of fittings See ASHRAE Equivalent Lengths
Fundamentals of Hydronic Design Differential Pressure - Fittings Equivalent Length, in Feet of Pipe for Common Fittings Ex.: 2 90 o elbow is = 5.5 ft of 2 copper tube Copper Tube Sizes Equivalent Length, ft. Fitting 3/8" 1/2" 3/4" 1" 1.25" 1.5" 2" 90 o elbow 0.5 1 2 2.5 3 4 5.5 45 o elbow 0.35 0.5 0.75 1 1.2 1.5 2 Tee (straight run) 0.2 0.3 0.4 0.45 0.6 0.8 1 Tee (side port) 2.5 2 3 4.5 5.5 7 9 Reducer Coupling 0.2 0.4 0.5 0.6 0.8 1 1.3
Differential Pressure - Fittings Flow, q w = 33 USgpm 2 Copper Fittings 4 Elbows 2 Pump Adapters 2 Manifold Adapters p Pipe + Fittings Head Loss in Fittings (4 x 5.5) + (2 x 1.3) + (2 x 1.3) = 22 + 2.6 + 2.6 = 27.2 ft of pipe (27.2 /100 ) x 2.5 = 0.68 ft of head
Differential Pressure - Manifold Flow, q w = 33 USgpm 2 Copper Manifold Tee Drilled 6 ft across p Manifold??
Differential Pressure Flow, q w = 33 USgpm 2 Copper Manifold Tee Drilled 6 ft across Head Loss in Manifold 6 + 6 = 12 (12 /100 ) x 2.5 = 0.3 ft of head (Use manufacturers data if available ) p Pipe + Fittings + Manifold
Differential Pressure Pex & Valves Flow, q w = 33 USgpm 25 loops, 400 ft each What is the flow/loop? What Pex Diameter? p Radiant Loops??
Differential Pressure Flow, q w = 33 USgpm 25 loops, 400 ft each What is the flow/loop? What Pex Diameter? p Radiant Loops? Radiant Pipe and Valves 33 USgpm/25 loops 1.3 gpm/loop?
Differential Pressure With ¾ diameter & 1.3 USgpm Velocity is 1.6 fps (acceptable) @ 120 ºF, 0.01436 per foot (acceptable) Wirsbo demo
Fundamentals of Hydronic Design Differential Pressure Flow, q loop = 1.3 USgpm/loop Radiant Pipe 400 x 0.01436 ft/ft 5.7 ft p Pipe + Fittings + Manifold + Radiant Loops
Differential Pressure Valves Flow, q valve = 1.3 USgpm/loop What is the head loss through service valve? What is the head loss through balancing valve? p valves??
Fundamentals of Hydronic Design Differential Pressure Valves q w, USgpm 2 = p, psi Flow, q valve = 1.3 USgpm/loop ¾ Service valve C v = 6.3 C v 1.3 USgpm 6.3 2 = 0.04 psi p valves??
Fundamentals of Hydronic Design Differential Pressure Valves q w, USgpm 2 = p, psi Flow, q valve = 1.3 USgpm/loop ¾ Balancing valve C v = 1.6 C v 1.3 USgpm 1.6 2 = 0.66 psi p valves??
Fundamentals of Hydronic Design Differential Pressure Flow, q valve = 1.3 USgpm/loop Valves Service & Balancing Valves 0.043 + 0.66 0.7 psi 0.7 psi x 2.31 ft/psi = 1.62 ft p Pipe + Fittings + Manifold + Radiant Loops + valves
Fundamentals of Hydronic Design Differential Pressure Circulator Selection Circulator Data Item Value Unit Pipe 0.45 ft of head Fittings 0.68 ft of head Manifold 0.3 ft of head Pex 5.7 ft of head Valves 1.62 ft of head Pump Head 8.75 ft of head Pump Flow 33 US gpm
Fundamentals of Hydronic Design Balancing Manifolds
Fundamentals of Hydronic Design Differential Pressure Balancing Valves Do you need them if all loops are equal? Is the flow per each loop supposed to be equal? When do you need them? When do you not need them? How do you establish the amount of balancing? What happens if you don t balance? When we have control over the pressure, we have control over the flow, when we have control over the flow we have control over the system.
Fundamentals of Hydronic Design Differential Pressure Balancing Valves Do you need them if all loops are equal? When do you need them? How do you establish the amount of balancing? p 400 x 0.01436 ft/ft 5.7 ft p 300 x 0.01436 ft/ft 4.3 ft 5.7 4.3 = 1.4 ft = 1.4 / 2.31 = 0.6 psi
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