Cycle Data Decoding Guide

Samsung EHS heat pumps report telemetry through two SmartThings components: an outdoor unit (compressor, ambient conditions) and an indoor unit (water circuit, pump, flow). Each component's cycle data is a hex-encoded binary blob that varies in length depending on the device model.

Different device models produce different data lengths with subtly different byte layouts. Dwellsee uses a binaryId-keyed architecture to select the correct byte layout for each device:

1. If the device's binaryId (firmware identifier) is recognised, use its registered byte layout
2. Otherwise, fall back to a length-based heuristic (24, 31, or 36 bytes)
3. If neither matches, return null (unknown format)

Samsung EHS heat pumps have a temperatureReference setting that controls what the indoor temperature sensor measures:

The temperatureReference setting is reported by the samsungce.ehsTemperatureReference capability. To correctly decode flow temperature for all devices, check this value and use byte[4] only when the reference is “air” and byte[4] is not 0x05.

Outdoor data length varies by device (18 or 28 bytes). Both formats share the same byte positions for the first 18 bytes.

Position:  0  1  2  3  4  5  6  7  8
           ^^^^^ ^^^^^ ?? ^^       ^^
           |     |     |  |        |
           |     |     |  |        outdoor temp (byte − 55)
           |     |     |  discharge temp (byte − 55)
           |     |     constant 0x5E (purpose unknown)
           |     target compressor freq (int16 BE, Hz)
           current compressor freq (int16 BE, Hz)

Used by INDOOR components (SAC_EHS_MONO, SAC_EHS_SPLIT, SAC_DVM_HE). Flow rate is encoded as an integer.

Position:  0  1  2  3  4  5  6  7  8  9
           ^^ ^^ ^^    ^^       ^^ ^^
           |  |  |     |        |  |
           |  |  |     |        |  pump speed (byte = %)
           |  |  |     |        flow rate (LPM, integer)
           |  |  |     flow temp (byte − 55, air-ref only)
           |  |  return water temp (byte − 55)
           |  evaporator OUT temp (byte − 55)
           evaporator IN temp (byte − 55)

Used by INDOOR1 components on the TP1X platform (TP1X_DA_AC_EHS_01001_0000). Flow rate has decimal precision.

Position:  0  1  2  3  4  5  6  7  8  9
                 ^^ ^^          ^^ ^^
                 |  |           |  |
                 |  |           |  pump speed (byte = %)
                 |  |           flow rate (byte / 10 = LPM)
                 |  flow temp (byte − 55)
                 return water temp (byte − 55)

Used by INDOOR1 components on the S905D3 platform (S905D3_SAC_EHS_24, e.g. Samsung E50AJTAE1). Shares the same prefix layout as the 31-byte format with 5 additional trailing bytes.

Cycle data does not update when the system is off. When both the main system switch and heating circuit are off, the hex data is stale and reflects the last active reading.

This has important implications for consumers of decoded data:

• Flow rate should be set to 0 when the system is off, regardless of what the hex data contains
• Outdoor temperature may also be stale and should not be treated as a live reading
• When the system turns back on, it may take one polling interval (typically 5 minutes) before fresh data appears

Each decoded field has been validated or cross-referenced using one or more of the following methods: