Hot Water Circulation

Based on the hot water supply system characteristics, the following methods can be used. Method A and Method B are basically for small systems. The heat loss method (Method C) is more accurate. The calculation procedure is described in detail in the book, "Engineered Plumbing Design", by Alfred Steele. It is especially useful for larger systems. However, because of its complexity for manual calculation, it is not widely used in plumbing system design. Then, Method D is introduced as an Excel template by using VBA.

A. Estimating Flowrate by Number of Risers:

Size of Riser	No. of Risers	Flow, L/m
25 mm or less		1.893
32 and 38 mm		3.785
50 mm and larger		7.570

B. Estimating Flowrate by Fixture Units (FU):

FU	Flow, L/m
	3.785

C. Estimation of Circulation Flowrate by Heat Loss:

Table 1. Piping Heat Loss
(watt per lineal meter for 60°C water and 21°C room temperature.)
Nominal Pipe Size	Insulated Pipe (13 mm Fiberglass)	Bare Pipe
Nominal Pipe Size	Insulated Pipe (13 mm Fiberglass)	Sch. 40 Steel	Brass, Copper, T.P.	Type K Copper
13	14	34	25	18
19	16	41	31	25
25	18	51	37	31
32	20	62	44	37
38	24	70	51	44
50	27	87	62	56
64	31	104	72	65
75	37	124	87	78
100	44	157	109	99
125	53	191	133	122
150	61	224	155	143
200	77	287	193	181

Source: Converted from Engineered Plumbing Design, Alfred Steele, PE, CIPE

D. The Computer-Aided Hot- Water Circulation System Sizing

This VBA based template was introduced by Anjian Lu, CPD, and published on Plumbing System & Design magazine, Dec. 2004. By using this method, the required circulation flow rate and friction loss in the system are both calculated, so are the circulation pipe sizes and pump capacity.

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