Sizing The Heat Pump; Mono Mode Operation; Supplement For Dhw Heating In Mono Mode Operation - Viessmann VITOCAL Series Technical Manual

Design information

7.7 Sizing the heat pump

First establish the standard heat load Φ
sions with customers and for the preparation of a quotation, in most
cases estimating the heat load is adequate.

Mono mode operation

According to EN 12831, the heat pump system in mono mode must,
as sole heat source, be able to cover the entire heat demand of the
building.
For mono mode operation, the potential outside temperatures at the
installation site and the heat pump application limits must be taken
into account:
For minimum air inlet temperature and minimum flow temperature,
see chapter "Application limits to EN 14511".
Please also note that, in mono mode, the heat pump heating output
and the maximum secondary circuit flow temperature are influenced
by the outside temperature. This can result in comfort losses, for
DHW heating in particular.
Therefore please note the following design points:
■ Check whether the maximum heat pump flow temperature, ach-
ieved at the prevailing outside temperatures, fulfils the local DHW
heating requirements.
■ During commissioning or service, the secondary circuit tempera-
ture may lie below the required minimum heat pump flow tempera-
ture. The heat pump compressor does not then run independently.
■ If frost protection mode is permanently enabled (e.g. in a holiday
home), the secondary circuit temperature can drop below the mini-
mum heat pump flow temperature. The heat pump compressor
does not then run independently.
As a result, even with a mono mode heat pump design, an additional
heat generator must always be included in the design; e.g. an
instantaneous heating water heater.
If the heat pump cannot meet the heat demand in mono mode, then
the heat pump must be operated in mono energetic mode (with
instantaneous heating water heater) or in dual mode (with external
heat generator). Otherwise you run the risk of the condenser icing
up, causing significant damage to the heat pump.
Note
Depending on type, the instantaneous heating water heater is either
integrated in the heat pump or available as an accessory.
See chapter "Installation accessories".
Sizing is of particular relevance to heat pump systems that are to be
operated in mono mode, since oversized equipment frequently
incurs disproportionate system costs. Therefore avoid oversizing!
When sizing the heat pump, observe the following:
■ Take into account supplements to the heat load of the building to
cover power-OFF periods. [In Germany] the power supply utility
may interrupt the power supply of heat pumps for up to 3 x 2 hours
within a period of 24 hours.
Observe additional individual arrangements for customers with
special tariffs.
■ The building inertia means that 2 hours of power-OFF time are not
taken into consideration.

Supplement for DHW heating in mono mode operation

Note
In dual mode operation of the heat pump, the heating output availa-
ble is generally so high that this supplement does not need to be
taken into consideration.
VITOCAL
(cont.)
of the building. For discus-
HL
As with all heating systems, determine the standard heat load of the
building to EN 12831 before ordering the appropriate heat pump.
Note
The ON periods between 2 power-OFF times must be at least as
long as the preceding power-OFF time.
Estimate of the heat load based on the heated area
The heated surface area (in m 2 ) is multiplied by the following specific
heat demand:
Passive house
Low energy house
New build (to EnEV)
House (built prior to 1995 with standard thermal insu-
lation)
Older house (without thermal insulation)
Theoretical sizing with power-OFF time of 3 × 2 hours or when
used in Smart Grid
Example:
Low energy house (40 W/m 2 ) and a heated area of 180 m
■ Estimated heat load: 7.2 kW
■ Maximum blocking time of 3 × 2 hours at a minimum outside tem-
perature in accordance with EN 12831
24 h, therefore, result in a daily heat volume of:
■ 7.2 kW ∙ 24 h = 173 kWh
To cover the maximum daily heat volume, only 18h/day are available
on account of the times when the power supply is blocked. The
building inertia means that 2 hours of the period during which power
is blocked are not taken into consideration.
■ 173 kWh / (18 + 2) h = 8.65 kW
In other words, the heat pump heating output would need to be
increased by 20 % if the power supply were blocked for a maximum
of 3 × 2 hours per day.
Frequently, blocking times are only invoked if there is a need to do
so. Please contact the customer's power supply utility to enquire
about blocking times.
For a general residential building, a max. DHW demand of approx.
50 l per person per day at approx. 45 °C is assumed.
■ This demand represents an additional heat load of approx.
0.25 kW per person given a heat-up time of 8 h.
■ This supplement will only be taken into consideration if the sum
total of the additional heat load exceeds 20 % of the heat load cal-
culated to EN 12831.
2
10 W/m
2
40 W/m
50 W/m 2
80 W/m 2
120 W/m 2
2
7
VIESMANN
117