Is there a reliable and fool proof occupancy sensor for WCs out there

[MikeSharp01]

We are approaching 1st fix wiring and I am wondering about many things but one thing, toilet occupancy, is leaving me with this question. To avoid me over thinking this, I can imagine all kinds of scenarios, I thought I would ask it here. The device will need to control the MVHR boost mode and reliably detect occupants even if they are still for extended periods.

[JohnMo]

Toilets normally have a quite high flow rate from MVHR in terms of air changes per hour, unless you have a huge toilet.

 

Any smells are gone in minutes without boost.  If really concerned, put a manual boost switch outside the door by the light switch.  So if anyone feeling guilty about the smells they can hit a boost switch.

[Radian]

Doppler works best for detecting people. The classic example being that it can resolve heartbeats. Either microwave or ultrasound is suitable. Some alarm sensors combine microwave and PIR for false trigger protection. Used to be able to get very small detectors (microwave only) for putting in cars.

[Adam2]

I'm just about to install Aeotec 7 sensors (zwave) which are wireless (or can main power) to turn on bathroom lights and if presence detected for>3 mins run boost on the MVHR for 10 mins. Timings of course are flexible. MVHR has a boost signal which I'm connecting to a zwave relay. For showers I'll see how well the MVHR humidity sensor works and if not fast enough may experiment with humidity comparisons between bathrooms and adjacent bedrooms - probably not necessary but I like to experiment 🙂 These sensors I used already to test motion and trigger lights etc - very impressed. But of course this needs a hub to control the logic but I enjoyed learning about that (hubitat elevation) 

  

[Russdl]

I’m with @JohnMo on this, probably unnecessary.

 

We don’t have any automatic boost control for the bathrooms/toilet and don’t feel that it’s something we should have done. 

[MikeSharp01]

On 26/06/2022 at 14:22, Radian said:

Used to be able to get very small detectors (microwave only) for putting in cars.

Thought I would get one of these to play with: https://www.unmannedtechshop.co.uk/product/24ghz-mmwave-radar-sensor-fall-detection-module/

 

2 minutes ago, Russdl said:

We don’t have any automatic boost control for the bathrooms/toilet and don’t feel that it’s something we should have done. 

Does your your normal extraction rate meet the building regs requirement purge / etc?

 

Edited July 1, 2022 by MikeSharp01
Typo

[Russdl]

Just now, MikeSharp01 said:

Does your your normal extraction rate meet the building regs requirement purge / etc.

In a nutshell, no. 

[Radian]

2 hours ago, MikeSharp01 said:

Thought I would get one of these to play with: https://www.unmannedtechshop.co.uk/product/24ghz-mmwave-radar-sensor-fall-detection-module/

 

That's a nice find! Could do with a couple of those round my Mums house.

[MJNewton]

9 hours ago, Adam2 said:

For showers I'll see how well the MVHR humidity sensor works and if not fast enough may experiment with humidity comparisons between bathrooms and adjacent bedrooms - probably not necessary but I like to experiment

 

For what it's worth I've been using a duct-mounted DHT22 humidity sensor to detect a >5% rate-of-rise in humidity (over five minutes, measured across the whole house extraction) and in the few years we've had it running not observed a single false positive or negative. The 5% was intended just to be a starting point but it's turned out to be perfect.

 

You can see from the graphs how prominent the spikes are (the first three are showers, the fourth a pan of boiling water) and so quite easy to detect without being triggered by more gradual variations:

 

Edited July 1, 2022 by MJNewton

[joth]

2 hours ago, MJNewton said:

 

For what it's worth I've been using a duct-mounted DHT22 humidity sensor to detect a >5% rate-of-rise in humidity (over five minutes, measured across the whole house extraction) and in the few years we've had it running not observed a single false positive or negative. The 5% was intended just to be a starting point but it's turned out to be perfect.

 

You can see from the graphs how prominent the spikes are (the first three are showers, the fourth a pan of boiling water) and so quite easy to detect without being triggered by more gradual variations:

 

 

My Zehnder has built in humidity detection and automatic boost, which works ~ok for cooking and showering, but doesn't help one jot for toilet stink bombs

 

 

Regarding occupancy detection, I have really basic PIR in each bathroom: https://www.aliexpress.com/item/1005003500901521.html £6 (I opened them up and removed the clicky clicking relay, as the transistor can drive Loxone digital input directly).

These are totally fine for turning on lights, especially low level night lights and they're sensitive enough to keep the lights on while having and long soak in the bath

I could use them for MVHR boost and towel rad but I find in practice triggering those from the temp sensor on the shower is more useful.

 

i don't have a specific solution for the stink bomb, and honestly it hasn't been an issue.

 

 

[Pocster]

In all seriousness a cctv camera will give a perfect solution in a toilet ….

[JohnMo]

5 hours ago, MJNewton said:

 

For what it's worth I've been using a duct-mounted DHT22 humidity sensor to detect a >5% rate-of-rise in humidity (over five minutes

 

What is the DHT22 tied into to signal the MVHR to go into boost?

[MJNewton]

35 minutes ago, JohnMo said:

What is the DHT22 tied into to signal the MVHR to go into boost?

 

There's a script running on a Raspberry Pi doing the monitoring which in turn signals a Shelly smart relay to trigger the MVHR's boost input.

[Radian]

CO₂ Is also a good option I've not seen mentioned. Especially in a smallish room. They used to be very expensive but an IR one like this is similar in price to the microwave sensor.

RS232 output and plenty of Rpi and Arduino libraries - although I use one with an ESP8266 running Tasmota to get MQTT from it...

 

[MJNewton]

Do you monitor humidity levels too @Radian? I seem to recall reading somewhere that CO2 levels generally correlate with humidity level and whilst I couldn't quite see why that would necessarily be the case I did wonder if my humidity (only) monitoring might suffice for determining air 'quality'. At £22 I am tempted by that sensor you linked to though.

[SteamyTea]

45 minutes ago, MJNewton said:

Shelly

That should be a Smelly considering the job it is going to do.

[Radian]

1 minute ago, MJNewton said:

Do you monitor humidity levels too @Radian? I seem to recall reading somewhere that CO2 levels generally correlate with humidity level and whilst I couldn't quite see why that would necessarily be the case I did wonder if my humidity (only) monitoring might suffice for determining air 'quality'. At £22 I am tempted by that sensor you linked to though.

I've never really tried using either as an occupancy sensor. The CO2 sensor is in a room that we tend to receive visitors in and gives me a silent reminder to open a window if levels go above 800ppm. 

Here's an old thread about CO2 sensors used with MVHR:

 

[MikeSharp01]

On 01/07/2022 at 08:49, Radian said:

That's a nice find! Could do with a couple of those round my Mums house.

Got one (Well similar) and thought I would have a dig around the amplification of the IF stage to make it read with arduino / EPS. Anyway found this video - some of this chaps gear will make you jealous I think the Keysight MXA is around $80K. Insightful video. 

 

[Radian]

Oh boy, Keysight MXA - 10 Hz to 50 GHz - will have a gander at that video for sure.