eta ePE-K 140, Installation Manual

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General information Buffer storage tank
8 Buffer storage tank
8.1 General information
Finely adjustable radiator valves and fresh water
module
The lower the return temperature to the buffer, the
greater its heat storage capacity. The buffer utilisation
of radiators can be improved considerably with very
finely adjustable thermostat valves (kvs less than
0.35).
With a fresh water module, the hot water supply can be
integrated in the buffer to save space, and a solar
heating system can also be integrated with the buffer
very simply and effectively.
Buffers for multi-boiler systems
For systems with several boilers and also for those
with several very different heating circuits (especially
different times of operation or air and underfloor
heating in the same heating system), a bypass is
needed between heat producers and consumers to
ensure stable hydraulic conditions for the individual
circuits. A hydraulic bypass is nothing more than a pipe
connection between the flow and the return with the
same diameter as both. The differential water
quantities from heating and boiler circuits flow through
this bypass, This results in a neutral pressure point that
ensures that the heating circulation cannot influence
the boiler water circulation and vice versa.
A bypass that can do more than just stabilise pressure
conditions is the buffer. If a wood boiler for the base-
load range and an oil/gas boiler for peak load or as
emergency reserve are operated together in a heating
system, a buffer storage tank reduces the operating
time of the peak-load boiler by compensating for brief
differences between production and consumption. The
number of boiler starts/stops when consumption
fluctuates around the rated output of a boiler is
reduced, saving energy and easing stress on the
boiler.
To work as an output compensator and bypass for
several boilers, the buffer's storage capacity should be
chosen to match 20 to 30 minutes of full-load operation
for the largest automatic wood boiler in the system. In
special cases, peak loads and non-continuously
operated air heating systems must also be taken into
account, or the morning peak if the start of an oil/gas
boiler is to be avoided. Whereby "first", the morning
peaks themselves should be minimised with staggered
starting times for the heating circuits as well as
reasonable set-back temperatures.
Choosing buffer size for systems with automatic
fuel supply
Even if some subsidy guidelines demand "litres per
kilowatt" and thereby specify a minimum buffer size,
one should arrange for a technically correct size. The
storage capacity of a buffer essentially depends on the
spread between the heating system's boiler flow
temperature and return temperature.
Example: For a 90 kW boiler with 70°C flow tempera-
ture, 30 minutes of full-load operation with underfloor
heating and 30°C return temperature (= 40°C spread)
requires a buffer volume of 968 litres, but with radiator
heating and 50°C return temperature (= 20°C spread),
it requires 1,935 litres.
The minimum volume for the buffer can also be
calculated with the following formula:
Switzerland: Air Quality Control Regulation
In Switzerland, the Air Quality Control Regulation
"LVR" requires that heating boilers have a minimum
volume for heat accumulators (buffer). For the calcula-
tion, a distinction is made between manually and auto-
matically operated boilers.
•
For a manually operated boiler (e.g., log boiler) up
to 500 kW rated capacity, there needs to be at
least 12 litres of buffer volume for each litre of fuel
filling chamber. The volume must not exceed
55 litres per kW rated capacity.
Which is why a SH30 boiler (150 litres filling
chamber) needs a buffer volume of 1800 litres
(=150x12). A SH60 (223 l filling chamber,
223x12=2676 l) requires at least 3300 litres
(=60x55) buffer volume.
Volume =
operating time (h) x output (kW) x 860
spread (°C)