Danfoss RA-DV Fact sheet [da]

Technical Article - hydronic balancing

New ways of balancing two-pipe systems

How to achieve superior hydronic balance in heating systems by utilising the Danfoss Dynamic Valve™ type RA-DV and the Grundfos MAGNA3 speed controlled pump

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Introduction

Low energy consumption in buildings is not something which comes easy. Ensuring that the components in a heating system work together is a pre-requisite when we want low heating bills. A means of ensuring low energy consumption is to balance the heating system correctly, and this article will explain how the new Danfoss Dynamic Valve™ type RA-DV and the new Grundfos MAGNA3 speed controlled pump work together superbly to achieve this.

We will first look at how we compensate for the variations in partial, and how the requirement to balance the heating system means we need to control flow; and to obtain this, we need to control the differential pressure across valves as well.

We will show how this can be done by utilising the Danfoss Dynamic Valve™ type RA-DV in combination with the Grundfos MAGNA3 variable speed controlled pump, looking at an installation in Fredericia, Denmark, where 60 apartments in a 10 storey building has heating supplied from a system consisting of two Grundfos MAGNA3 pumps serving two mixing loops, each supplying 10 raisers, each

of which has manual balancing valves of Danfoss type MSV mounted. This installation showed that utilising the speed controlled Grundfos MAGNA3 pump and Danfoss Dynamic Valve™ type RA-DV in combination ensures problem free operation of a heating system.

Heating systems need to be commissioned properly to ensure high comfort and lowest possible cost of operation. In earlier days commissioning was a complicated matter where lots of different valves and measuring tools needed to be utilised for proper commissioning.

The difference today is that designated flow can now easily be set on each radiator and pump set point by means of the new Danfoss dP tool™ (for measuring differential pressure)

in combination with Grundfos GO (offering mobile access to Grundfos online tools). Not only does this ensure pump optimisation and lowest energy use, it also reduces time for commissioning substantially.

The challenge: balancing two-pipe systems

The uneven distribution of heat	Or to put it in another way, a heating
between units – single radiators or	system is in balance when the flow
apartments – in a heating system	in the whole system corresponds to
is what we refer to as a balancing	the flow rates that were specified for
problem. A heating system is balanced	the design of the system. This is a key
when an even distribution of hot water	challenge for many two-pipe systems.
is ensured thereby ensuring maximum
comfort at minimum running cost.	Let us first look at the general
	challenge in operating two-pipe
	heating systems. The load profile below
	shows how load is changing during a
LOAD	heating season in Europe. In only 420
LOAD	hours out of 7000 heating hours do we
	need 100% capacity from our heating
	system.

100%

75%

50%

25%

HOURS

428 1050	2450	3080
6% 15%	35%	44%

In order to compensate for the variations in load, we equip our systems with thermostatic valves on each radiator. The thermostat will reduce the flow through the individual radiator and ensure the required room temperature is maintained.

As pressure loss increases by the square of flow, the differential pressure across the first radiator valves is substantially higher than it is at the last consumer, as shown in the illustration below.

RAD	RAD	RAD
1	2	3
p a.	p b.	p c.

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