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

dynamic.danfoss.com

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.

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.

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.

2

The challenge: balancing two-pipe systems

The uneven distribution of heat
between units – single radiators or
apartments – in a heating system
is what we refer to as a balancing
problem. A heating system is balanced
when an even distribution of hot water
is ensured thereby ensuring maximum
comfort at minimum running cost.

LOAD

100%

75%

50%

25%

Or to put it in another way, a heating
system is in balance when the flow
in the whole system corresponds to
the flow rates that were specified for
the design of the system. This is a key
challenge for many two-pipe systems.

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
heating season in Europe. In only 420
hours out of 7000 heating hours do we
need 100% capacity from our heating
system.

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.

RAD RAD RAD

1 32

∆p

a.

HOURS

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.

∆p

b.

∆p

H

c.

a.
b.
c.

Q

3