In this guide you will learn how the estimated savings shown in the Smart Weather Compensation reports in Leanheat® Monitor are produced: what they are based on, the formula behind them, and how the end of season forecast is made.
Why flow temperature and not heat meter readings
The most obvious way to measure a saving would be to read a heat meter. In practice heat meters are rarely connected to the ECL controllers, while flow temperature data is always available in Leanheat® Monitor.
We also know precisely what effect SWC has on the flow temperature, because SWC is what applies the offset. Basing the calculation on flow temperature therefore gives a reliable figure and lets us serve every ECL customer rather than only those with a connected meter.
The principle
Heat consumption is estimated from the flow temperature: a high flow temperature indicates high consumption, and a low one indicates low consumption.
SWC applies an offset to the flow temperature setpoint based on the weather, for example lowering it on a sunny day. That reduces the temperature difference between the radiator and the room, which lowers heat dissipation and therefore energy consumption. Every change is logged, and the monthly saving is calculated by comparing the average requested offset against the situation with no offset at all.
The formula
Heat transfer from a radiator to the room can be expressed as:
Q = (Tf - Tr) x A x h
where Q is the heat transfer, Tf the flow temperature, Tr the room temperature, A the surface area of the radiator and h the heat transfer coefficient.
Writing this out for the situation with SWC and the situation without it, the surface area and the heat transfer coefficient are the same in both, so they cancel out. The room temperature is also roughly the same in both. What remains is a ratio that depends only on the temperature difference, which simplifies to:
Saving % = Offset / (Tf + Offset - Tr)
Here Offset is the average SWC offset for the month and Tf is the resulting average flow temperature. For calculation purposes a constant room temperature of 22°C is assumed.
A worked example
Suppose the average SWC offset for a month is 1.5°C and the resulting average flow temperature is 50°C. The calculation is then:
1.5 / (50 + 1.5 - 22) = 1.5 / 29.5 = 5.1%
This is why a modest looking offset of one or two degrees still produces a saving of several percent: what matters is the offset relative to the difference between flow and room temperature, not the offset on its own.
Space heating only
All estimated savings consider space heating only. SWC does not affect domestic hot water or any other heat consumer, so those are not part of the figures. When you compare an SWC report against a heat bill, remember that the bill includes consumption SWC never touches.
How the forecast is made
Savings from SWC depend largely on the weather, so a forecast for the rest of the heating season cannot simply extend the current trend. Forecasted savings are calculated using the average historical weather conditions for each controller's location for the remainder of the season, combined with each controller's own past performance.
This is why the forecast bars in the SWC Performance Report can differ noticeably from the realized ones: a mild sunny spring will beat the historical average, and a cold one will fall short of it.
What to expect
Verified savings in space heating consumption are in the range of 5 to 15%, confirmed across hundreds of buildings in Central and Northern Europe. For an individual building the figure depends on the characteristics of the building, the local weather and the existing heating system configuration, so treat the range as the expected span rather than a guarantee for any single site.