07 August 2014

Hand warmers and hot water bottle

When working from our home office I have committed to, wherever possible, warming myself rather than warming all the air around me.

The office is often the coldest room in the house and I have spent a lot of time there this winter. Besides wearing warm clothes (including ugg boots) and often wrapping myself in a blanket, I also started to put a hot water bottle under my feet at the desk. I am amazed at how successful this is at keeping me warm. One hot water bottle, wrapped in a towel, lasts a whole work day.

I also purchased hand warmers from our good friend Megan of Granny Funk Crochet.

Sometimes I will also warm a heat pack in the microwave and sit it in my lap for a while in the morning when it is most cold, or if I am working at night. With these aids, I virtually never turn a heater on for the office. I think better with cool air on my face, so these are both sustainability and productivity measures.

Initial Time: Boiling a full kettle for a hot water bottle takes about 5 minutes. Purchasing hand warmers involved some emails with Megan and a few days to wait for delivery.

Initial Cost: Extra hot water bottles purchased recently cost $12.95 each. They now have covers made out of cut up old jumpers, and I also wrap my office foot-warmer one in an old towel - no cost. Hand warmers were $30. Or you could sign up for one of the Granny Funk crochet classes and learn to make them yourself.

Ongoing time or cost commitment: Five minutes for the hot water bottle each time. A cost saving due to reducing the amount of energy used for heating (see below).

Impact: Boiling a full kettle of water (1.75L) when the temperature is 10°C uses approximately 661.5kJ of energy, or 0.184kWh ('units' in our system) - 184Wh, or about the same as leaving a 60 Watt light bulb on for three hours. (see my previous kettle post for the formulas). Microwaving a heat pack (wheat bag) uses around 42Wh to give warmth for about two hours.

When all attempts to warm myself with body heat, clothing and a hot water bottle fail, I use an electric oil-fin heater. This is a 1000W device, but as I would never run it flat out and it heats a confined space, the actual use is less than this. If I were to run it for nine hours of work day, it would use approximately 3.5kWh.

Using one boiled kettle instead of the oil fin heater for a day of warmth saves over 3kWh (units) a day, around 2.5kg of carbon dioxide every winter work day. 

Running the reverse cycle air-conditioner in our living area to warm enough house to reach the office is hard to measure, but the office is the far corner of the house from the aircon. A fairly conservative guess would be 5-6kWh per day to use the reverse cycle to heat the office, which is why we don't do that.

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