Smart Grid, Mini-split heat pumps, and energy control

Looking for ideas on this project. Below is a letter to one of my contacts at Schneider. I hope it will be of help to someone!


Hello Roy,

I just wanted to thank-you for the informative webinar on the CSW the other day. We may have met before at one of the Trace/Xantrex shows a ways back. My name is Dave Angelini and I heard you say in the webinar you like challenges. First I would like to give you some background on me. I am an electrical engineer from the Test and measurement industry, Aerospace, and Marine electronics.

My Wife and I have been offgrid for 23 years and I run a small business called Offgrid Solar that is world-wide consulting and some local work up here in the California Sierra mountains near Yosemite national park. I have over 70 happy offgrid homes under my belt. I also have worked with Xantrex Jeff Everett on the mppt-60 controller and beta tested with Jeff Fieldhouse on the mppt-80-600.

Here is what I am looking to do. I want to be able to run a Mini-split heat pump and control it so that when clouds start to build up it can throttle down the energy consumption. On the face it does not sound that hard but first some background. I was one of the first to do this for myself and my clients 7 years ago. The mini-split is the best use of excess energy that I know of for heating and cooling when the battery is charged or charging.

The way they work is when the programmed room temp is the same as the actual room temp they run using as little as 10 watts and up to their first power tier of about 300 watts. The second tier occurs when the differential between actual and programmed is about 2 degrees. At this point the mini-split can use between 400 and 500 watts. The last tier is when the differential gets to about 4 degrees and then the minisplit will consume about 800 watts. This data is from a 12,000 BTU / 1 ton unit with a SEER (seasonal energy efficiency requirement) of over 30. That is the current state of the art. The data will vary with size/SEER and it is here as an example.

Schneider has their smart grid equipment called Wiser. I have contacted the engineers there and while the Wiser system can turn-on or turn-off and set the temperature of a heat pump, it is not smart enough to throttle the thermostat up or down based on some other parameter such as voltage or ???. When I was working with Jeff we talked about a smart inverter that would know what the solar resource was (data from MPPT’s) and use the Aux to throttle up/down a thermostat, if there was one like this. There is always the catch as it is quite a bit harder to do this than it appears. I have made this short in hopes that you might know someone or like to get involved with this.

The project can lend itself to more than offgrid as I have customers who are XW based grid-tied and want to run max cooling or heating and not use the grid. When I hear the term Smart Grid I always think that my project here really is the Holy Grail of using renewable energy efficiently in all weather conditions. Most of my clients run 4 KW of tracked solar and want to set the desired temperature and leave the home knowing that if clouds come in and degrade the solar the system will not drain the battery much. They want just as much for the system to know the clouds have left and resume the heat pump conditioning space. A clunky Aux driven/solenoid shutting down the heat-pump is just too clunky, involves electricians, and really is not a smart use of energy as much is wasted in this strategy.

Thanks Roy! Hope you have a good week-end!
Dave Angelini / Offgrid Solar webpage below
http://members.sti.net/offgridsolar/