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Renewable Energy: Solar DHW and Energy Conservation: Towards Whole Systems Analysis

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    I'm trying to get a better handle on the whole systems analysis of DHW and Solar Hot Water. The goal, if possible, is to show that water/energy efficiency measures plus SHW is cheaper that a Business As Usual model (I accept that simple efficiency will offer the least cost solution).

    Is anyone aware of any studies that examine in detail 1) DHW use (litres/day or m3/annum) 2) actual the energy and water savings from efficiency features and design.

    Ideally such studies would also cover heat losses from the DHW systems pipe work (adding insulation to pipes being and efficiency measure), elimination of dead legs etc.

    Any help appreciated.

    Mark
    • CommentAuthortony
    • CommentTimeOct 23rd 2007
     
    You may into new territory here?

    Insulating domestic hot water pipes may not be an energy efficiency measure overall! Commercially and systems with pumped primary circuits yes. In a house all the heat lost from hot water pipes should be lost to indoors and thus is supplementing the heating input. The heat lost is much less in summer but summer is not so warm as we would like to think nor for very long. That is the time when insulation may have better benefit.

    To look at hot water heat losses in isolation from the overall picture of where it is going and what it is used for (airing clothes etc) is missing a little something.

    Using less water would produce far bigger savings than anything else. This could be seen as economy or a reduction in quality of life by some.

    Cold water detergents and washing powders have huge potential for saving whole power stations -- I surprised they are not given away by the big producers.

    Solar -- these systems are becoming very much more cost effective than ever before and using direct electricity or fossil fuels to make water hot is looking ungreen
  3.  
    Tony,
    By "water/energy efficiency measures" (in my mind) I included spray taps, low-flow showers, efficient washing machines, efficient dishwashers (can use less water the issue is whether or not electric heated; if elec then hand wash is better....unless SHW) etc. I added insulation to the list simply because 1) keeps water hotter for longer thus minimising standby losses 2) in a very low energy house lack of insulation to pipes could result in cooling loads, not because I considered it to be "the solution."

    DHW accounts for 6% of commercial office and 22% of residential energy use. As I am sure that you will recognise, to develop an understanding of the whole system you need to analysis the component parts.

    Also note that the title of the post includes "Towards Whole Systems Analysis" i.e. I recognise that this is not a complete view of water use or energy use. I am trying to develop a study of a particular facet of energy use (DHW) and acertain what reduction in water use compared to a Business as Usual Model will mean that Joe Bloggs is financially no worse off than using a) elec heated DHW b) gas heated DHW. A capital saving is a capital saving so : -

    cost of saved water + cost of saved energy = affordable* cost of SHW

    *where affordable means financially no worse off than would have otherwise been the case.

    Mark
    • CommentAuthortony
    • CommentTimeOct 25th 2007
     
    Sounds like a good project. there will be a lot of consumer resistance to low flow showers -- they all want high flow (=high cost) ones. Ungreen ones too.

    Re insulation of hot water pipes -- say someone uses the kitchen sink then goes out for the rest of the day. The pipe from the hot supply to the sink will be full of hot water. Whether or not it is insulated, by the time they return all the heat from the pipe will have escaped into the building. Insulation will slow down the loss of heat but it will not stop the heat being lost. I cant see the point in insulating. Also the same applies to cooling loads the heat will escape into the house either over a few tens of minutes or over a few hours the but note that the total heat loss will be the same insulated or not.
  5.  
    Tony,
    I agree that the heat will be lost, can't deny the physics. By slowing the rate of heat loss from the pipes in a super insulated home the peak cooling load can be reduced. Also when people get home from work they use hot water intermittently. The insulation will mean that the water is warmer for longer thus avoiding the occupant running (wasting) water that has become cold.
    I'm not saying that vast quantities of energy are lost in this manner, or that the losses can not serve a function i.e. space heating. Water efficiency is the first stop, and probably the last stop for many. The idea is to study it map it all out and then assess the most economic solutions. Intuition tells the us a great deal but hard data offers reassurance and helps to convince skeptics about the value of these measures (even if it is, sadly, just based on the economics.)

    So the question remains: is anyone aware of any studies/surveys that examine water use and more specifically domestic hot water use?

    Mark
  6.  
    Mark

    This study has some great data, it may be of help? Wrong country though!

    http://www.branz.co.nz/main.php?page=HEEP
  7.  
    Thanks Jeff. Sadly couldn't quite find what I was looking for though ;-(
    Mark

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