eta PelletsCompact PC33, Руководство по установке

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Buffer storage tank General information
27
8 Buffer storage tank
8.1 General information
At low heating loads, either install a buffer or set
short heating time slots
For very well-insulated brick walls (not for wooden con-
struction), the house itself is an excellent thermal
store. If the boiler output is too high, it can be adjusted
to the house's heating requirements by limiting the
heating time to three short time slots spread over the
day.
If there is very low heat consumption during the transi-
tional period in autumn/spring (e.g. heating only in the
bathroom), then a buffer storage tank is needed for this
low heating load.
Wooden houses need a buffer storage tank
For a wooden house with radiator heating, where there
is not even the screed of an underfloor heating system
to act as a thermal store, the installation of a buffer
should be considered.
With a design output less than 70% of the boiler's rated
output, an underfloor heating system operating only
with time slots will cause large temperature variations
in the rooms and a buffer storage tank is required. Heat
produced by the boiler and not currently needed in the
house can be stored in a buffer storage tank and
returned to the heating system when needed.
When is a buffer storage tank necessary?
A buffer has to be installed for the boiler under the
following conditions:
•
if individual room temperature control is installed.
• for more than two heating circuits.
• especially in apartment buildings where the flats
are individually controlled.
• in low-energy houses, when a substantial portion
of the boiler's operating time is spent below its
output range.
• during the transitional period in autumn/spring
when there is very low heating demand, such as
only for the bathroom.
• for wooden houses with low heat capacity and
radiator heating.
• if above-average hot water demand or high spikes
in hot water use are expected, e.g. in hotels, blocks
of flats, showers in sports facilities. A pellet boiler
needs up to 20 minutes (wood chip boiler up to
45 minutes) to reach its maximum output from
standby.
• if an air heating system is to be started without
warm-up time for the boiler.
• if a solar heating system is being integrated with a
low-temperature heating system (underfloor
heating).
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.
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:
Volume =
operating time (h) x output (kW) x 860
spread (°C)