Section 3: System Controls In A Domestic Setting; Boiler Inter Lock; Horstmann Prt Thermostat; Heat Pump Controller - Dimplex LA 6 MI Installation & Technical Manual

Section 3: System controls in a domestic setting

Boiler inter lock

The Domestic heating compliance guide sets out the best
practise for preventing energy wastage by preventing
unnecessary running of the circulation pump and heat
pump.
External controls should include:
 Room thermostat to regulate the space
temperature and interlocked with the heat
 Timer to optimise operation of the heat
pump unit operation.
pump
An interlock is defined as "controls which are
wired so that when there is no demand for
either space heating or hot water, the boiler
and pump are switched off.
The use of Thermostatic radiator valves
alone does not provide interlock.
Figure 3: Extract from Domestic Heating compliance guide,
V1 April 2006

Horstmann PRT thermostat

The LA MI range of heat pumps achieves boiler interlock
using the PRT thermostat.
Supplied by Horstmann, the mains powered thermostat is
designed to provide an economical but comfortable
pattern of heating without the need for complex
adjustments by the user. With built in minimum room
temperature protection this thermostat is ideal for use with
heat pumps because it maintains a base level of heat.
For day-to-day use only the 3 large buttons on the front of
the thermostat are required. The centre „WARM/COOL‟
button, complete with Braille markings, changes the
temperature state and the „+‟ and „-„ buttons provide fine
user adjustment as well as audible feedback. Each user
adjustment is immediately reflected in changes to the
bright red and blue LED display.
Using a variety of pre-installed heating profiles that can be
easily set up by the installer, and a minimum cool setting
of 15C, the ThermoPlus aims to provide maximum
comfort to the user and prevent hypothermia and keep a
level of background heat. Under the flap the blue standby
button will put the control into „frost protection‟ mode until
reactivated.

Heat Pump Controller

The heat pump‟s safe and efficient operation is regulated
by the built in controller. The remote panel can be
connected via the 15m cable meaning allowing the user to
adjust the heat pump settings.
Recommended controller settings can be
found in the installation instructions. An
explanation of how to set the controller can be
found in the programming overview document.

Weather compensation

The highest flow temperatures are only required during the
coldest weather. As the external temperature increases,
the heat loss of the build decreases which means that the
heat emitters no longer have to work at their maximum
output in order to keep the building at the correct
temperature.
The LA MI is fitted with a weather compensation curve as
shown in Figure 4. The curve can be adjusted depending
on the system characteristics. By activating weather
compensation it ensures the heat pump is always
operating at the minimum flow temperature and therefore
the maximum efficiency.
Figure 4: Weather compensation curve on the LA MI
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