Hello.
I’m interested in building an openHAB compatible power control module that people could use to control things like water heaters, electric heat etc. The need is that in my area solar PV tariffs favor consuming energy rather than feeding it back into the grid so if there was a way for people to control and consume generated electricity it would make solar PV more economical to install.
The overall plan involves this control module being available for use and passing various safety certifications, some kind of openHAB integration to monitor energy flow in/out of the house, hopefully using data from the solar inverter without additional hardware, and software on the openHAB system to use the energy flow and things like Internet connected thermostats in order to control the heater modules. The story is a bit simpler for the electric hot water heater use case.
Does this sound interesting to you? If so, let me know if you’d like to be involved or have any questions.
Hello Chris,
Would you like to measure the energy consumption directly with the control module, or are you considering interfacing with existing energy meters (pulse generators, KNX, Modbus, etc.)?
I am currently working on a controller that has a small energy measurement part (for power less then 1 KW, but can be upgraded using transformers). I might have a bit of an input, but I guess I need more details on what you would like to achieve in terms of controller inputs/outputs.
Best regards,
George
Hi George.
In this case I was thinking that the overall energy consumption could be measured by the pv inverter itself. Many of them have CTs on the mains that enable them to determine how much energy is flowing in/out of the main panel. They also usually have RS485 interfaces available. I was thinking the openHAB server would be nearest the inverters both for mains power and to get access to the RS485.
For the device downstream of the power control module I’d imagine some configuration would let you set a wattage or voltage/amperage as a one time setup. The module would be hard wired inline with the power for the device so a one time configuration didn’t seem to be a critical step.
For the overall system knowing the consumption of each device would let the openHAB controller determine if there is sufficient additional energy to activate the device, and external inputs to determine if it was necessary.
For instance the control module would support a thermal sensor that could determine the temperature of your hot water heater. If there is sufficient pv generated energy you’d turn the device on via the power control module and reevaluate once it was on. If you had additional power you might activate HVAC or electric heaters, if you needed to heat/cool your home.
I did think of adding power monitoring to the module and it may make sense to do so. I was also looking what that might take in terms of complexity and cost and for a commercial product it would help to keep the cost down.
Hi Chris,
The exact power consumption per individual consumer can be determined only if you have energy measurements for each consumer (that means that the control module should be installed in the electrical distribution panel). In terms of a commercial product, as long as you do not certify the energy measurement part as a precise energy measurement device, I do not think it should require a lot of costs (take a look at MSP430F6736 - a 1Euro IC, maybe a total of 10-20Euro per measurement channel). For the temperature side, integrating sensors is very cheap nowadays (less than 2-3 euros per channel).
Having openhab as decision maker, is great in terms of integration with other systems.
If you need more detailed help on the hardware, PM me.
Best regards,
George
Hi George.
Wouldn’t it be possible to look at the device label to determine consumption? If the PCM was installed to control an electric heater you could read the heaters labeling and use that to set the consumption value in the PCM. Then the openHAB scripts could use that value. You could almost have the openHAB sw learn the consumption. If you turned on the heater you could look at the energy flow monitored by the pv inverter and the change in flow would correspond to the energy drawn by the device.
Clearly that wouldn’t work for all kinds of devices, and hot water heaters can have two different heating elements.
The goal is to consume the solar PV energy so it doesn’t reach the grid, in order to get the highest value vs. the credit from the utility company. Where I’m located electricity costs X but you are credited for generated electricity at roughly 0.3 * X. If you had a high level power flow measurement in/out of the mains you could almost get away without knowing anything about device power consumption, but at least you could learn the consumption by looking at the change in energy flow and then make use of that to consume what you could.
I’ve been looking at using the ESP-WROOM-32 as it supports wifi and bluetooth connections and pretty low cost.
I was looking at designing the module to handle 240V @ 25A, or 6000 watts continuous. That should provide margin for electric hot water heaters. It might make sense to build different versions if they can be built for less by reducing the power capacity. That would let people choose the appropriate module for their own use.
Hi Chris,
Reading the labels is indeed a solution for 1 or two stages heaters/coolers. When modulated heaters/coolers are switched on, the whole energy consumption based on labels becomes a fortune teller approximation (just to understand the amount of variables - for a 11 KW labeled VRF system, I recorded values between 0,5 to 8 KW).
About the ESP-WROOM-32, I would not tinker with wi-fi and/or bluetooth especially when measuring energy on values that exceed 200W due to possible electromagnetic interference (especially when you will have it connected next to the power wires or in the heater). I would suggest having a lower bandwidth to avoid possible interference (KNX has a very good isolation). Thus said, I would probably opt for a controller interfaced with an existing product. Moreover there are switching devices with integrated energy meters (take a look at Schneider/Merten KNX switch actuators with current detection) - very helpful when you need to disconnect one or multiple loads if your scenarios require it. In conjunction with the inverters’ RS-485 communication, you can have a nice power controller.
Best regards,
George
