More data on solar air heater

The recent cold snap let me collect some interesting new data. Previously I had reported on temperatures in the building with the solar heat on and off, but that didn’t tell how much energy was being captured by the collector. At the end of that post I speculated on a way to approximate measuring the energy.

Each day during the cold snap I read the power meter at 10:30pm. The Weather Depot website gave me the Heating Degree Days for each day. (Heating Degree Day is the indoor temperature minus average outdoor temperature; a measure of how much heating is needed. Colder days have more HDDs.)

This gave me a table, and I could calculate a ratio HDD/KWH which should be a constant

HDD (55F indoor) KWH/day Ratio
52 62.44 0.839
42 51.32 0.824
33 39.75 0.825

The ratio lets me predict, knowing the HDDs, how much energy the building would use.

I turned the solar on Wed, and collected data. It was a fairly clear day, high haze but strong shadows. If the solar is effective it should save me energy, ie, reduce the KWH that would be expected to be used for a given number of HDD

It Worked!  The Solar heater came on for 4-5 hours. While I never saw the temperature inside rise above the 55F thermostat setting, I used 6 KWH fewer than the HDD on Wednesday would predict.

6 KWH is 22% savings – about 1/4 of the energy, which roughly agrees with the collector operating for 1/4 of the day. The building has no thermal storage, its like a greenhouse that warms up in the sun and cools again when the sun sets.

The water heater portion of the system is the way I will store energy. I hope to do a final system leak test on that system this Saturday.

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4 Responses to “More data on solar air heater”

  1. New Years Resolution Jan. 2014 | One small step for man Says:

    […] Thoughts about learning outside the university « More data on solar air heater […]

  2. scspaeth Says:

    I’ve been making progress on development of a data acquisition system. In a browser, I can monitor and/or log analog sensor values (e. g. temperature and light) to a file on an SD card that can be pulled from the micro controller and read as a CSV file on computer or uploaded to an online spreadsheet.

    In an email message, you said,
    “Steve, better data. I got 6KWH energy via the collector. Have not returned to the materials you sent but realize I need to run some more data lines before I finish sheetrock downstairs.”

    How many sensors are you hoping to measure?

    • Nils Peterson Says:


      Thanks for the comment in the blog and for doing it in public where others might learn of your efforts to create an open source data logger.

      I’m glad to hear there is an embeddable microcontroller and an SD card, so I don’t need to devote a PC to the task.

      The number of channels is a balancing act, with cost (I presume) being the downside. 4 channels would give me lots to work with, for different experiments I could even reconfigure the sensors.


  3. 2015 Resolution – Reflect on Conservation | One small step for man Says:

    […] I have some more data on the impact of the solar air heater in the Cookhouse. My previous report was from a short duration observation. Now I have a year’s worth of data which appears to […]

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