{"id":129,"date":"2008-08-18T07:55:45","date_gmt":"2008-08-18T05:55:45","guid":{"rendered":"http:\/\/www.retro.co.za\/blog\/?p=129"},"modified":"2008-08-18T12:10:41","modified_gmt":"2008-08-18T10:10:41","slug":"some-basic-jacuzzi-mathematics","status":"publish","type":"post","link":"http:\/\/www.retro.co.za\/blog\/?p=129","title":{"rendered":"Geek Alert : Some basic jacuzzi mathematics"},"content":{"rendered":"<p>It takes one kilo-calorie to heat 1 litre of water by 1 degree C. A calorie is 4.184 joules. In science-speak : &#8220;The specific heat capacity of water is 1 cal\/gram-C or 4.184 Joule\/gram-C&#8221;.<\/p>\n<p>A Joule is also a Watt-second. Which relates to the well-known kilowatt-hour by a factor of 3 600 000.<\/p>\n<p>In mathematical terms :<\/p>\n<p>Q = mc(DeltaT) : m = mass, c = specific heat capacity, deltaT = amount you want to heat the water (or anything else) by. The important thing is that all the units match, to get Q in Joule you need c in Joule\/gram-C.<\/p>\n<p>The optimal jacuzzi temperature seems to be <a href=\"http:\/\/www.epinions.com\/content_2276106372\" target=\"_blank\">39C (102F)<\/a>. So if the water is at 15C, deltaC = 24.<\/p>\n<p>And thumbsuck : the typical jacuzzi is around 1000 litres.<\/p>\n<p>Q = 1000 x 4184 x 24 (Note the sly dropping of the decimal from 4.184 &#8212; this is because we&#8217;re working with litres not grams, a liter of water weighs 1000 grams) = 100416000 Watt-seconds = 27.89 kWh. Which at the current 47.38c\/kWh equates to just over R13.<\/p>\n<p>And with a 4kW element, this will take almost 7 hours. Of course this ignores any losses, anything that&#8217;s warm wants to cool down, so it will take more energy and time to actually heat the jacuzzi to 39C.<\/p>\n<p>I&#8217;m contemplating keeping the thing at say 25 degrees or so, that won&#8217;t lose too much heat to ambient and it&#8217;s halfway there, energy and time speaking.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>It takes one kilo-calorie to heat 1 litre of water by 1 degree C. A calorie is 4.184 joules. In science-speak : &#8220;The specific heat capacity of water is 1 cal\/gram-C or 4.184 Joule\/gram-C&#8221;. A Joule is also a Watt-second. Which relates to the well-known kilowatt-hour by a factor of 3 600 000. In mathematical terms : Q = mc(DeltaT) : m = mass, c = specific heat capacity, deltaT = amount you want to heat the water (or anything else) by. The important thing is that all the units match, to get Q in Joule you need c in&#46;&#46;&#46;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[31,4],"tags":[85,39],"class_list":["post-129","post","type-post","status-publish","format-standard","hentry","category-geek","category-house","tag-house","tag-jacuzzi"],"_links":{"self":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts\/129","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=129"}],"version-history":[{"count":0,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=\/wp\/v2\/posts\/129\/revisions"}],"wp:attachment":[{"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=129"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.retro.co.za\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}