[Greenbuilding] [BULK] Re: Baxi Luna question

[Drew A. Gillett, P.E.]

small gas heaters are inefficient( nominally 65% but typically less than 40%) , lossy (large loss for small volume of water stored), dangerous (relying on natural draft ventilation in tight homes is risky) .  they are cheap lowe(r)'s or home despot  $200 and you throw them away when they break, adding to landfills

the reason your fossil fool usage is low is you don't use much hot water. more power to you. i prefer longer showers, having the water hot at the tap more or less when when i want it (after all that is the purpose) doing the laundry and not having a fit when guests or my niece stop by to use the free hot water.    your 45 therms (by the way do you have a separate gas meter on your water heater or are you inferring the use?) would heat about 4500 gallons per year or only 12 gallons per day. we are heating 20 to 60 (measured , do you measure your hot water usage?)  . 

backup fossil energy usage in solar can be made arbitrarily small by making the system larger. size is limited by the pocketbook . a good system budget these days is 6666 dollars as that is where the fed tax credit stops. in states with additional credits ( nm, me, ma) more should be spent.. typical systems return in kwh about 20 to 40 times what they use in pump and controller energy and in modern systems this is provided directly by pv renewably.  i argue strongly for smart solar with minimal backup and control and pumping energy. this is of course predicated on efficient use of the water thru reduced consumption and more insulation. many of the tankless units have high electrical parasitic losses from pumps and blowers and controls. . 

my 600 kwh is the direct thermal equivalent of about 18 therms.   most utilities use a mix of nukes, coal, oil gas and renewables. we buy green tags so ours is wind.

were you to switch to solar you would save 60 to 90 % (perhaps 100% if you waited for sunny days as you seem to be willing to do) of your admittedly small usage.  you would have a small solar system . with small costs. 

keep burning your fossil fuel inefficiently as you are, keep polluting , keep fueling climate change.  you are only a little bit pregnant.
  

  ----- Original Message ----- 
  From: Reuben Deumling 
  To: Drew A. Gillett, P.E. 
  Cc: Greenbuilder list 
  Sent: Wednesday, June 20, 2007 8:46 PM
  Subject: Re: [Greenbuilding] [BULK] Re: Baxi Luna question


  I'm neither frozen nor dead, and the sun is shining. Your objections to small gas-fired tank water heaters are evidently strong, but you haven't said what they are. 

  I have no interest in disparaging solar water heating systems per se, and am very grateful for your willingness to share your meter-data. Nevertheless I think it worthwhile to acknowledge the non-negligible backup energy commonly utilized with such systems. If one household's need for hot water can be met with an amount of fossil fuel comparable to another household's solar water heater's backup energy--as your figures seem to confirm--then this seems worth at least recognizing. For the record, our annual water heating energy has varied from 16 to 60 therms over the past ten years, depending on easy access to the pilot light. As I calculate it, the thermal equivalent of that amount of natural gas at a power plant would be about 150-600 kWh. 

  Put another way: were I to switch to your solar water heating system I would save no fossil fuels. Most people most of the time have no way of determining this since it is rare that such systems are submetered. In my view people contemplating different water heating systems should be apprised of at least the potential for such a result. 

  Reuben Deumling


  On 6/20/07, Drew A. Gillett, P.E. <deaneg at hotmail.com> wrote:
    as i have posted before, my now nearly 30 yearold system has been running 500-700 kwh of backup electric per year.  it has supplied about 80% of our hot water for a family of 2-6 during that period.  it's still does biweekly laundry for my niece. 

    it is 80 sq.ft of flat black thin copper  single fibreglass cover with 120 now 80 gallon tank with a separately metered 6kw element in the top 15 gallons of the tank.  it has been reported on numerous times.  the stuff works.  solar displaces fossil fuels with clean renewable energy at  a cost and maintenance that people can afford. 

    small gas fired tank units are about the worst you can do.

    freezing to death in the dark is not what it is about reuben.