Solar Hot Water

[Phil Squire]

Hi folks

Anyone got any leads or links to find out the “best” timer/temperature settings for a SHW system? I’m thinking about settings for someone who is not a geek and will want the system to run automatically and get the most out of the system.

Cheers, Phil

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[Jo Wills]

Hi Phil
I asked my friend and ex-Energy Options employee Marcus Baker, he has lots of experience with SHW, this is what his response was:

The electrical element is best used at the end of the day so the sun can do the most work possible and if the cylinder is still not adequately heated the electrical element can boost it. So having the timer activate the element at 4pm and off again at 5.30pm or 6pm would usually be adequate if the solar is doing it’s job. This should only really be needed in winter and to a limited extent in spring and autumn, depending on weather. So being able to over-ride the timer and have it off completely when the sun is doing all the work will give maximum savings.

If there is a high demand for hot water or small cylinder size then a timer could also activate in the morning for a brief period but this isn’t ideal as you want to enter the new day with cold water at the bottom for optimum solar panel efficiency.

Regarding temperature, I’m not sure what they mean but usually the electrical element would be set to 60’C for boosting.

I would love for Marcus to have access to the Hub, he has an absolute wealth of knowledge and is now working independantly, and quite isolated…

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[Norman Smith]

There are a number of sources and on-line discussion sites, see below. I believe this is a situation where an in-depth conversation is needed with the household about how they live, occupancy and hot water use patterns. The best solution – hot water energy services required at least cost – can be proivided by a combination of generic guidelines and specific advice for the household,  with an understanding of the kind of hot water system, etc.

Cheers, Norman

http://www.econation.co.nz/hot-water-temperature.html#.UZ1AcEp-T4Q

http://www.ecobob.co.nz/forum/ForumPosts/5078/Re-Cylinder-thermostat-settings.aspx?ShowForumPostId=5085

http://www.eeca.govt.nz/sites/all/files/action-sheet-3-hot-water-july-2011.pdf

http://www.powerswitch.org.nz/powerswitch/site-info/saving-energy

http://www.mitre10mega.co.nz/ask_an_expert/interior/hot_water_cylinder_timer_/?expert=1804

http://www.cea.co.nz/Highelectricitycosts

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[Andrew Pollard]

Hi Everyone,

In order to set a timer on a SWH system you’ve first got to have one to set!

Looking at this issue back in  2007 only 20% of the 33 systems I looked had a timer installed on the cylinder element. It is important to distinguish the control of the cylinder element from control of the circulation pump as if you don’t control the element it may reduce the efficiency of the system dramatically (Adrian Kerr has done modelling of this).

In looking to retrofit a timer to a badly configured solar system I was alarmed at the cost (over $150) for a fuse board mounted timer unit (if it was a plug-in version you’d get something at the Warehouse for under $20)

The other part of topic (setting temperatures) is a bit of the a long story. There is some risk awareness needed here.  It would be nice if could tell people to set this themselves (but not below a Legionella risk level) rather than advising them to consult an electrician (all of those dangerous wires to avoid). Perhaps consumer adjustable thermostats should be compulsory??

Cheers
Andrew

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