Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Hot Water Circulation System - Return Pipes

Hot water can be circulated through a return pipe if it's instantly required at the fixtures.

Sponsored Links

A return circulation pipe is sometimes provided in a hot-water system where it is desirable to have hot water available continuously at the fixtures. Typically for systems where the distance from the hot water heater to the consumption fixtures exceeds 25 - 30 m.

Time for Hot Water to reach Fixture without Circulation Pump

Time for hot water to reach fixture

  • 1 US gpm = 0.0630 liter/sec
  • 1 feet = 0.305 m

Hot Water - time to reach fixture - liter per second

Hot Water Circulation Pump

Hot water circulation system with return line

A smaller pipe with an inline pump is connected to a point close to the most distant fixture and to a point close to the hot water heater. The pump can run continuously or intermittent circulating enough water to keep the temperature drop in the pipeline during low or no consumption within an acceptable limit. 

The required circulated water flow can be calculated 

Q = q / (ρ cp dt)                                        (1)

where

Q = pump capacity (m3/s)

q = heat loss from the pipe line (W)

ρ = density of water (kg/m3) (988 kg/m3 at 50 oC)

cp = specific heat of water (J/kgoC) (4182 J/kgoC at 50 oC)

dt = temperature drop (oC)

Typical heat loss from an insulated pipe line is in the range 30 - 60 W/m. Acceptable temperature drop can be 10 oC.

Example - Required Circulation Volume in a Hot Water Return Pipe Line

The length of a pipeline inclusive the circulation line is 100 m. With water at temperature 50 oC the average specific heat loss from the pipe line is estimated to 30 W/m. The total heat loss from the whole pipe line can be calculated as

q = (100 m) (30 W/m)

  = 3000 W

Required water flow to limit the temperature drop to 10 oC can be calculated as

Q = (3000 W) / ((988 kg/m3) (4182 J/kgoC) (10 oC))

   = 7.2 10-5 m3/s

   = (7.2 10-5 m3/s) (1000 liter/m3)

   = 0.072 liter/s

Sponsored Links

Related Topics

  • Water Systems

    Hot and cold water service systems - design properties, capacities, sizing and more.

Related Documents

Sponsored Links

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

Citation

This page can be cited as

  • The Engineering ToolBox (2016). Hot Water Circulation System - Return Pipes. [online] Available at: https://www.engineeringtoolbox.com/hot-water-circulation-return-pipe-d_1918.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter

















































2.27.11

Sponsored Links
.