Danfoss Flow and Difference Pressure Optimize Guide Fact sheet

Technical Paper

Flow and Difference Pressure Optimize Guide

Introduction	Between 80 and 90 % of all buildings in Northern	In 2-pipe heating systems a correct dimensioning
	Europe have heating systems with little or no	and adjustment of the valves is a prerequisition
	hydronic balancing.	for achieving optimal energy consumption and
	The results are:	high user comfort.
	• Discomfort due to underor overheating	By spending a few minutes on studying this
	• Discomfort due to noise problems	paper you will be ready to use RA-DV Dynamic
	• High energy costs	Valves™.

Balancing a	The purpose of balancing a heating system is to
heating system	optimize the flow and get as good a heat con-
	sumption as possible.
	To achieve this we have to make sure that the
	right amount of water is distributed to the
	radiators, as well as the pump pressure or setting
	of the differential pressure regulator is correct.
	Balancing - installation - performance
	1. Exact calculation of the heating output,
	or
	2. Estimation of the Heating output:
	• Get drawings with room sizes in m2 of all flats.
	If drawings are not available a laser range
	finder can be used for measuring the areas.
	• Select the heat loss.
	• Calculate the flow.
	• Determine preset values for​ each radiator
	valve according to the calculated flow. Find
	the selected preset in the Presetting table (see
	next page).
	• Decide together with the property owner or
	caretaker limitations and the current room
	temperature. Consider the need for thermo-
	stats with remote sensor.
	• All radiator valves must be preset.
	• Fill with water and bleed the system.

Fig. 1: Pressure and flow changes

Fig 2: Comfort with hydronic balancing

VFGWG102

© Danfoss

05/2014

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Technical Paper	Flow and Difference Pressure Optimize Guide
Tables	1. Heat loss (empirical values)
	Year of	until		1959-	1969-	1974-	1978-	1984-	1995-	from
	construction	1958		1968	1973	1977	1983	1994	2001	2002
	Single family house	180 W/m2		170 W/m2	150 W/m2	115 W/m2	95 W/m2	75 W/m2	60 W/m2	40 W/m2
	Townhouse:
	- at the end	160 W/m2		150 W/m2	130 W/m2	110 W/m2	90 W/m2	70 W/m2	55 W/m2	35 W/m2
	- in the middle	140 W/m2		130 W/m2	120 W/m2	100 W/m2	85 W/m2	65 W/m2	50 W/m2	30 W/m2
	Multi family house:
	- up to 8 floors	130 W/m2		120 W/m2	110 W/m2	75 W/m2	65 W/m2	60 W/m2	45 W/m2	33 W/m2
	- more than 8 floors	120 W/m2		110 W/m2	100 W/m2	70 W/m2	60 W/m2	55 W/m2	40 W/m2	33 W/m2

2. Difference flow and return temperature

Typical values (K)

∆t (K) Heat source

10-15 Heat pump

15-20 Low temperature boiler

20-25 Condensing boiler

25-40 District energy, indirect

3. Presetting

RAW	RA2000	living/TWA	Presetting
15	20	25	1
20	25	30	2
30	30	35	3
40	40	45	4
50	50	60	5
70	75	80	6
90	95	100	7
110	125	135	N

Example
	Building type							Multi family house
	Year of construction								1984
	Room size								40 m2
	Number of radiators in the room								1
	Heat effect needed							55 W/m2 (according to table 1)
	Difference flow (ΔT) needed							20° C (according to table 2)
	Formula:	=		(W/m2) x m2 x 0.86	= ..... l/h			=	55 x 40 x 0.86	= 94.6 l/h
				∆t (K)					20

Presetting should be 7 (according to table 3, with RA2000).

Presetting of more radiators in the room

Two radiators in the room of same size should be preset to:

	94.6	= 47.3 l/h = presetting 5 (with RA2000)
	2

Are the radiators of different sizes, the presetting should be calculated according to each radiator’s area coverage.

Further calculation possibilities concerning the radiator performance as well as the heat loss offers the Danfoss Heating App and the DanBasicSoftware.

Note!

Corner rooms, rooms with ceiling towards the outside and without heated floors, walls and concrete deck directly on soil requires slightly more effect from the radiator to provide the same comfort as in other rooms (raise the presetting with 0.5 compared with a normal room).

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VFGWG102

© Danfoss

05/2014