Weather-Compensated Heating Control with Night Setback

Matching the flow temperature to the outside temperature (heating curve) and lowering it outside occupancy hours.

How does weather-compensated heating control with night setback work?

With weather-compensated control, an outdoor sensor measures the outside temperature and the controller derives the appropriate flow temperature from it via the heating curve: the colder it is outside, the warmer the heating water. The heating curve is described by its slope (gradient) and level (parallel shift). If it is set too steep or too high, the heating runs at an unnecessarily high flow temperature; this increases boiler, distribution and standby losses. Occupancy time programmes complement the control in the time dimension: outside occupancy hours – at night, at weekends, during holidays – the flow temperature is lowered or the heating switched off entirely. Modern controllers and building management systems also calculate the optimum start time so that rooms are warm again by the start of occupancy.

Which buildings benefit from optimising the heating control?

The effect is greatest in non-residential buildings with clearly defined occupancy hours – office buildings, schools, nurseries – which are often kept at comfort temperature around the clock although they are only used 40 to 60 hours per week. In apartment buildings, too, a correctly set heating curve brings noticeable savings. Requirements are a controller with outdoor sensor, either existing or retrofittable, and a modulating or variably controllable heat generator. With heat pumps, a flat heating curve setting is particularly important because every kelvin less flow temperature reduces electricity consumption; night setback should be moderate here to avoid expensive reheating.

What does optimised heating control actually deliver?

In residential buildings, heating energy demand falls by 5 to 12 %, in non-residential buildings by 10 to 20 %. An office building with a space heating demand of 200,000 kWh and no previous occupancy time programme saves around 33,000 kWh of natural gas and about 6.7 t of CO2 per year. Costs range from 200 to 1,500 € for re-setting an existing controller to 5,000 to 15,000 € for a new controller or connection to a building management system. Over a 12-year service life, payback is 1 to 3 years.

Energy carrier

Erdgas, Heizöl, Pellet, Strom → Erdgas, Heizöl, Pellet, Strom

Savings potential

5-12 % (Wohngebäude), 10-20 % (Nichtwohngebäude)

Worked example

An office building with 2,000 m² of usable floor area has a space heating demand of 200,000 kWh per year, met by a gas boiler with an efficiency of 0.90. Until now, the heating has run without an occupancy time programme: at night, at weekends and during holiday periods, the building is heated at the same flow temperature as during office hours. As part of the optimisation, the heating curve is adjusted to actual demand and a time programme with setback outside occupancy hours is configured. For a non-residential building without a previous time programme, the upper saving factor of 0.15 is applied. The final energy saving is 200,000 × 0.15 / 0.90 = 33,333 kWh of natural gas per year. With an emission factor of 0.201 kg CO2/kWh, this corresponds to about 6.7 t of CO2 annually. Since only the existing controller is reparameterised, the measure pays back within a few months.

Investment & payback

200-1.500 € (Reglereinstellung) bis 5.000-15.000 € (neuer Regler/Klima-Computer) · Service life: 12 a · Payback: 1-3 a

Applicability

Requirements

Typical buildings

Frequently asked questions

How much does it cost to optimise a heating control system?

Re-setting an existing weather-compensated controller costs 200 to 1,500 €, depending on the effort for analysis, heating curve adjustment and time programmes. If a new controller with outdoor sensor or a connection to the building management system has to be installed, costs are 5,000 to 15,000 €. With savings of 5 to 20 % of heating energy, the measure pays back in 1 to 3 years.

How do you set the heating curve correctly?

The heating curve is set step by step: first the level is lowered until rooms are only just warm enough at mild outdoor temperatures, then the slope is adjusted based on cold days. Starting values are a slope of 1.2 to 1.6 for radiators and 0.4 to 0.6 for underfloor heating. Each change should be observed for a few days. All thermostatic valves must be fully open during this process.

Is night setback worthwhile with a heat pump?

With heat pumps, night setback is only worthwhile in a moderate form of 1 to 2 K. A large setback requires high flow temperatures in the morning for reheating, which significantly worsens the heat pump's efficiency. In well-insulated buildings with underfloor heating, thermal inertia is so great that setback has hardly any effect. With gas or pellet boilers in non-residential buildings, by contrast, a substantial setback makes sense.

What is the difference between weather-compensated and room temperature control?

Weather-compensated control sets the flow temperature according to the outdoor temperature via a heating curve and thus responds to the weather in advance. Room temperature control measures the temperature in a reference room and regulates accordingly – it captures incidental heat gains from sun or occupants, but only in that room. For buildings with several rooms and heating circuits, weather-compensated control is standard, often supplemented by individual room control.

Which standards apply to heating controls in buildings?

The key standards for heating control are EN ISO 52120-1 on building automation and ÖNORM H 5056 on assessing heating energy demand. EN ISO 52120-1 classifies control functions into automation classes and enables their impact on energy demand to be assessed. The method for calculating savings from control optimisation is described in the Austrian Energy Efficiency Guidelines Regulation 2016.

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