Posts: 2
Joined: Tue Jul 23, 2019 3:26 pm

Water temperature and pump control for pond - how?

Wed Dec 04, 2019 10:47 am

Hi there,

First: I am not new to RasPi (as an IT guy using it for monitoring an such stuff), but I am new to use the RasPi for sensors etc.

The following project is on our mind:
We have a pond where we have to control the water temperature (heating) as well as a pump.
Currently this is done using some low-level electronic devices, but unfortunately they do not work reliably.
I am wondering now, if/how this can be done with the RasPi.
As input we have two to three parameters:
- Water temperature (below 2 degrees Celsius is critical)
- Air temperature
- Optional: use weather forecast for temperatures in the future
As output we have two:
- Water heating spiral
- Water pump
Conditions are simple:
- Condition A (for heating): If water temperature is below 2 degrees Celsius AND air temperature is below 2 degrees Celsius: Water heating enabled
- Condition B (for pump): If current time is between 08:00 and 22:00 OR Condition A is true: Pump enabled

So basically, in summer the pump only runs during day time, in winter, the pump runs during daytime or when the temperature is critical (danger of freezing). Heating runs also if there is danger of freezing, but not if the air is already warmer then the water resp. warmer then 2 degrees Celsius (e.g. in the morning after a cold night).

Now my questions:
- What components can I use to turn on/off the heating and the pump (both 230V AC)? Something like a radio controlled relais / power plug? They are weather protected, so no need to be weather proof (but also welcome if you know one).
- Are there any good sensors for monitoring the water temperature? E.g. one which is usable directly via WiFi (but with reasonable battery life)? Or better one wired to the RasPi directly (which might require additional circuits? and also limits the placement of the RasPi).
- Is the DS18B20 the right choice as (outdoor) air temperature sensor?
- What software to use? HASS.io? OpenHAB? IFTTT? OpenSprinkler? It should be easy to view the sensor data and control the pump & heating manually if needed (switch from automatic to manual mode) - ideally via Web-Interface or even an App.

Many thanks for your comments!

Posts: 718
Joined: Mon Mar 19, 2018 1:18 pm

Re: Water temperature and pump control for pond - how?

Sat Dec 07, 2019 12:02 am

If you look for reliable, use an arduino with a temperature sensor and a pair of relay module.

You can make it report state (temperature, relay states) later by serial to a Pi or ESP8266, just keeping the control loop on a simpler device makes the whole assembly much more reliable.

Posts: 560
Joined: Tue Nov 05, 2019 2:49 am

Re: Water temperature and pump control for pond - how?

Sat Dec 07, 2019 1:15 am

I agree re: the Arduino. It'll be cheaper overall (no need for additional hardware to read analog sensors), and probably more reliable because it's just a way simpler system overall.

As for sensors you can use pretty much any off the shelf thermistors, it looks like your only inputs are temperature readings. Relays/contactors to control your pump and heater can be similarly off the shelf, as long as they're rated for the required current/voltage you're working with, interfaced with the Arduino through appropriate low voltage circuits.

There are tons of examples of relays controlled by Arduinos, no need to go in to detail here.

As for the code, what you're looking to do is quite simple from a logic standpoint, perfect for an Arduino project, and I'm sure you can find many similar projects to draw ideas from.

Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 223
Joined: Fri May 24, 2019 2:10 pm
Location: Cambridge UK

Re: Water temperature and pump control for pond - how?

Mon Dec 23, 2019 12:00 pm

Don't forget to add some hysteresis to your switching, ie switch pump off when water temp goes down to 2c, switch pump back on when water temp reaches 3c or something similar. You don't want the pump rapidly switching off and on if the water temp is at the transition point.

Return to “Other projects”