Electronic Heat Cost Allocators - Brunata

Electronic Heat Cost Allocators
- what to measure and where to be installed
The Danish Agency for Development of Trade and Industry issue Danish type approval certificates for German heat cost
allocators with German type approval certificates, despite the fact that the installation point on the radiator is both
wrong and unsubstantiated. This leads to incorrect readings, in particular in Danish heating systems with dimensioned
temperatures of 70/40/20-12 ºC. Nevertheless, the Agency has announced that the Danish type approval certificates will
be based on ”German experience and practise”.
By Managing Director, J.P.
Fischer Hansen (MSc Engineering),
Brunata a/s
Ideally, electronic heat cost
allocators are to meter the
emission of heat from every radiator
in the building. Thus, we
can set up the following:
E = Σ(Φ v
- Φ R
)Δτ (1)
E = ΣΦ HL
Δτ-ΣΦ LH
Δτ (2)
An electronic two-sensor heat
cost allocator makes it possible
to measure both:
ΣΦ HL
Δτ (heat energy from the
heating surface to the air in the
room)
and ΣΦ LH
Δτ (heat energy from
the air in the room to the heating
surface)
However, in order to render
an accurate measurement feasible,
the heat cost allocators
should be installed in a way
ensuring the necessary relation
between registration and
heat emission to be present as
required in the European Standard
EN/DS 834, 6.3. According
to the standard documentation
for each allocator brand
is required.
The radiator’s absorption of
heat from the room ΣΦ LH
Δτ (at
t L
>t m
) is not mentioned in the
standard. But it is necessary in
order to record the consumption
of heat (E) that the consumer
is to pay for.
Choosing the allocator’s
temperature range
To measure ΣΦ HL
Δτ and
ΣΦ LH
Δτ one should be able to
measure a room temperature
of 15 ºC or lower. In cases of
for instance frost-free garages
one must be able to measure
0 ºC as a minimum.
Especially in low temperature
systems it is important that
the allocator is able to ‘solve’
equation (1) correctly.
Therefore, allocators not capable
of measuring the contribution
ΣΦ HL
Δτ record for instance
heat from the sun or from
stoves. In order to avoid this
problem such allocators measure
F instead - F being a summation
of heat emission to the
air in the room. However, only
for one specific temperature:
F = ΣΦ HL
Δτ for ΔT > 5 K (3)
where T is the radiator’s average
temperature minus the
room temperature.
This must be regarded as an
E is the quantity of energy
Φ v
= added effect
Φ R
= effect return
Δτ = measurement period
In most cases the measurement
of E, on the basis of (1),
requires a heat counter consisting
of a flow meter, a temperature
sensor in both the
supply and return pipe and an
integrator on each consumption
branch in the system. An
expensive solution which often
is not technically possible.
Instead it is simpler and thus
cheaper to measure E as the
difference between the heat
emitted from the radiator’s
heating surface and the heat
absorbed by the heating surface
from the air:
UK-QB 10.1444/10.05.2004
Reprint of article from the Danish magazine ‘VVS’ volume 8, june 1998

E/R = emitted energy from the radiator per registered unit on the allocator
M/Mn= Volume flow through the radiator in proportion to the norm volume flow
(90/70/20). Radiator and allocator exponent = 1.3
‘emergency solution’ which
leads to significant registration
errors – in particular when it
comes to low temperature systems.
Due to the radiators’ low
average temperatures a considerable
part of the heat emitted
at low capacity (typically during
autumn and spring) will not be
recorded. Still, a considerable
part of the heat absorbed during
warm summer periods and
later on emitted will be registered
as consumption.
The allocators are to be approved
by accredited laboratories.
These laboratories are
designed and accredited for
allocator testing (3). But they
are not able to test allocators
using (2).
Documentation for the
installation point
In connection with new Danish
requirements on type approvals,
German laboratories have
turned out to have tested and
approved allocators without
checking wheather the installation
point, as stated by the
manufacturer, is correct. Even if,
according to the standard, this
must be certified.
All German allocators are installed
in 75 % of the radiator
height – regardless of make.
Used as “documentation” for
this installation point is an article
in the German magazine
“Heizung, Lüftung und Haustechnik”:
Montageart für HKV
nach dem Verdunstungsprinzip
(HLH 1980/6). I.e. an article
about evaporative heat cost allocators.
All German electronic
two-sensor allocators are also
installed in this incorrect position
of height, as the high point
of installation for evaporative
allocators must compensate for
decreased registration at low
capacity due to the relation to
the air temperature – a problem
which does not exist for electronic
allocators.
This has been clearly confirmed
throughout the last 30
years, during which Brunata
has carried out a number of
tests on the correct installation
point. It was, by the way,
Brunata’s own tests on the installation
point of evaporative
heat cost allocators which lead
to the tests referred to in HLH
1980/6. Brunata’s tests on
electronic heat cost allocators
can be seen in figure 2, which
shows three different installation
heights.
The Danish Agency for Development
of Trade and Industry
issue type approval certificates
based on German type approvals,
but they do not ask for
proper documentation as to
the point of installation. Thus,
Danish customers will have to
ask for special documentation.
When the installation point is
too high it implies that consum-
ers do not receive the reduction
in their heating bill to which
they are entitled if lowering
their consumption of heat. As
a result a significant part of the
incentive to lower ones heat
consumption disappears. In
consequence of this the cooling
may become inadequate in the
district heating system.
Conclusion
At the next revision the European
Standard must be changed.
It ought to focus more on allocators
measuring the heat
emission E. The present standard
focuses on German conditions
with relatively high dimensioned
temperatures for
heating systems (90/70/20).
A revised standard should open
the possibility for designing allocators
whose specifications
correspond to the conditions
under which they are used, for
instance dimensioned temperatures
70/40/20, which is the
case in Denmark. Furthermore,
the administrative practice
must be tightened so that allocators
in non-compliance with
the standard are not approved
by national authorities.