VentiReg

Home Assistant custom integration for curve control of supply air temperature on ventilation units (primarily Flexit), based on outdoor temperature — the way a heating curve / weather compensation works.

Cold outside → warmer supply air, warm outside → cooler supply air, with a linear transition between configurable breakpoints.

Supply air
 22°C │●─────╮
      │       ╲
 10°C │        ╰──────●
      └──┬────────────┬────► Outdoor temperature
        5°C          20°C

Contents

• Features
• Requirements
• Installation
• Setup
• Entities
• Graphical curve card
• The ventireg.set_curve service
• How the regulation works
• Troubleshooting
• Limitations
• License

Features

• Multi-point curve (at least 2 points), linear interpolation, flat (clamp) outside the end points.
• Everything configurable in the UI — outdoor sensor, climate entity, curve points, interval, tolerance, rounding step.
• Graphical card with drag-the-points editing (auto-registered, no build step).
• Auto-pause: if anything other than VentiReg changes the setpoint, regulation stops automatically (a manual change is never overwritten).
• Notification: persistent notification in Home Assistant 24 hours after auto-pause occurred.
• Switch for on/off, status sensor (On / Off / Auto paused) and a sensor for the calculated setpoint.
• Rounds the setpoint to 0.5 °C (Flexit step).

Requirements

• Home Assistant with HACS installed.
• A climate entity (climate.*) where the target temperature controls the supply air — typically from Flexit Nordic (BACnet) or a Modbus/ESPHome solution. Verify that climate.set_temperature actually moves the supply air setpoint on your unit (see Troubleshooting).
• An outdoor temperature sensor (sensor.*) with a numeric value in °C.

Installation

Via HACS (recommended)

1. HACS → Integrations → three dots in the top right → Custom repositories.
2. Paste https://github.com/oleost/VentReg, choose category Integration, and add it.
3. Search for VentiReg in HACS and install it.
4. Restart Home Assistant.
5. Settings → Devices & services → Add integration → VentiReg.

Updating

HACS → VentiReg → Update → restart HA. Do a hard refresh in the browser (Ctrl/Cmd+Shift+R) so the new card is loaded.

Manual installation

Copy custom_components/ventireg/ to config/custom_components/ in HA, and restart.

Setup

When you "Add integration" (and later via Configure) you set:

Field	Description	Default
Outdoor temperature sensor	sensor.* measuring outdoors	–
Ventilation (climate)	climate.* where target = supply air temperature	–
Curve points	outdoor:supply, separated by comma/newline, e.g. 5:22, 20:10	-5:23, 5:20, 10:18, 20:10
Update interval	Minutes between each computation	15
Tolerance	°C deviation regarded as an external change	0.5
Rounding step	Step the setpoint is rounded to	0.5

Curve points format: each point is outdoor_temperature:supply_air_temperature. Decimals use a period. Points are separated by comma, semicolon or newline. Examples:

-5:23, 5:20, 10:18, 20:10         # four points (default)
5:22, 20:10                       # simplest, two points
-20:23, -10:23, 0:22, 10:21, 20:15, 25:15   # multi-point

Settings can be changed at any time via Configure on the integration — without reinstalling anything.

Entities

The integration creates one device with the following entities (the actual entity_id may vary with the HA language — check under Devices & services):

Entity (typical id)	Type	Description
switch.ventireg_regulation	switch	On = active regulation. Off = stopped (manually or auto-paused).
sensor.ventireg_status	sensor (enum)	On / Off / Auto paused.
sensor.ventireg_calculated_setpoint¹	sensor (°C)	The setpoint the curve gives right now. Has the attributes curve_points, outdoor_temp and status (used by the card).

¹ The entity id follows your HA language. In English it is sensor.ventireg_calculated_setpoint, in Norwegian sensor.ventireg_beregnet_settpunkt. Check the actual id under Settings → Devices & services → VentiReg, and use it in the card/service configuration below.

Graphical curve card

The integration registers the card automatically as a Lovelace resource (the way HACS does) — you do not need to add a dashboard resource manually. It happens right after Home Assistant has started. (Requires an HA restart the first time; if you use YAML dashboards, see Troubleshooting.)

Add the card to a dashboard

Edit the dashboard → + Add card → search VentiReg Curve, or use YAML:

type: custom:ventireg-card
entity: sensor.ventireg_calculated_setpoint   # use your actual entity id (see note ¹)
title: Outdoor compensation curve

Card options

Field	Required	Description
type	yes	Must be custom:ventireg-card.
entity	yes	The calculated-setpoint sensor (the one with the curve_points attribute).
title	no	Card heading. Default "Outdoor compensation curve".
min_outdoor	no	Fixed left edge of the X axis (°C). Default about -25.
max_outdoor	no	Fixed right edge of the X axis (°C). Default about 30.
x_step	no	Outdoor-temperature snapping while dragging (degrees). Default 1.

Usage

• Drag each point freely — left/right changes outdoor temperature, up/down changes supply air.
• A point cannot cross its neighbours (the curve stays in increasing order). Y snaps to 0.5 °C, X to x_step (default 1°). While dragging, the point's outdoor° / supply° is shown.
• The change is saved when you release, via ventireg.set_curve.
• The dashed line shows the current outdoor temperature, and the dot shows the current setpoint ("ACT SP").

The card is just a nicer way to edit the curve — it can also be changed via Configure (text field) or the service below. All three paths write to the same setting.

The ventireg.set_curve service

Overwrite the curve points from an automation, a script or Developer Tools.

Parameter	Required	Description
entity_id	no	Any VentiReg entity of the instance. Can be omitted if you only have one instance.
curve	yes	String ("5:22, 20:10") or a list of [outdoor, supply] pairs.

service: ventireg.set_curve
data:
  entity_id: sensor.ventireg_calculated_setpoint   # your actual entity id
  curve: "0:23, 10:18, 20:10"

How the regulation works

Every 15 minutes (configurable), and only when the switch is on:

1. Read the outdoor temperature and compute the supply air from the curve (linear interpolation, clamped outside the end points).
2. Round to 0.5 °C.
3. Check first: does the climate setpoint deviate from what VentiReg last set (≥ tolerance)?
   • Yes → someone else changed it → auto-pause (switch off, status "Auto paused"), write nothing. After 24 h paused, a persistent notification is sent.
   • No → write the curve value to the climate entity and remember it.

Resume: turn the switch back on. VentiReg then resets the reference and writes the curve value immediately (doesn't wait 15 min), so it doesn't pause itself again.

Manual off (you turn the switch off yourself) produces no notification — the notification only applies to auto-pause.

Troubleshooting

The card doesn't show up / "Custom element doesn't exist: ventireg-card". Restart HA after installing/updating. The card is registered as a Lovelace resource right after startup; check Settings → Dashboards → Resources — /ventireg/ventireg-card.js should be listed. Then do a hard refresh (Ctrl/Cmd+Shift+R). If you use a YAML dashboard (mode: yaml), resources are managed in YAML — add the resource yourself:

# in the dashboard configuration (or lovelace: resources:)
resources:
  - url: /ventireg/ventireg-card.js
    type: module

The setpoint on the unit doesn't move. Confirm that climate.set_temperature on your Flexit actually controls the supply air. Test in Developer Tools → Services: call climate.set_temperature on the entity and see if the supply air changes. If your unit controls supply air via a number.* entity instead, open an issue.

It goes to "Auto paused" unexpectedly. Then something else (an app, another automation, a manual change on the panel) changed the setpoint by ≥ tolerance. Increase the tolerance if needed, or turn the switch back on to resume.

Nothing happens / status doesn't change. Check that the outdoor sensor has a valid numeric value (not unavailable/unknown), and that the switch is on. Look for "VentiReg" messages in the log.

Limitations

• _last_set (the reference for pause detection) is kept in memory and saved to disk, but an external change made while HA was down is not detected until the next normal cycle.
• The card lets you drag the points freely (outdoor + supply), but cannot add/remove points in the graph yet — use the text field under Configure to change the number of points.
• The interpolation is linear and clamps outside the end points (no extrapolation).

See CLAUDE.md for architecture and design choices.

License

MIT