[Greenbuilding] [BULK] Re: Low flow with tankless heaters

[Lawrence Lile]

I would still recommend tankless heaters.  I'd not go back to the days of waiting 45 minutes after my wife takes a long shower, with the slow tank heater. Inifinite hot water makes up for a lot of little annoyances. These problems I mention are definitely not showstoppers.  I would, however, recommend to your clients to not use a low flow shower head.  Go ahead and splurge on that fancy deluge shower head like you'd see in a luxury hotel.  Other than that, switching from tank to tankless is a minor adjustment.  
 
I am just trying to optimize the system, fishing for ideas that might make it more ideal without increasing energy use.  I want to have my cake and eat it too! 
 
There is no absolutely perfect technology.  Let them know that there are 2 major problems with tank heaters: energy use and recovery time.  There are two major problems with tankless:  Maximum flow rate might not support 2 showers at a time (for smaller units) and minimum flow rate might take some adjustments.  Energy use, by some estimates, is half, [see ensuing flame war for more detail] and you never run out of hot water!  Both of those are the big plusses.  
 
--Lawrence Lile

________________________________

From: David Bergman [mailto:bergman at cyberg.com]
Sent: Fri 11/17/2006 7:45 PM
To: Lawrence Lile; GREENBUILDING at listserv.repp.org
Subject: [BULK] Re: [Greenbuilding] Low flow with tankless heaters


This report is disturbing because I've been recommending tankless (electric) heaters for current clients - and I wouldn't to have them dissatisfied (and complaining to me about it).

Have others experienced these problems? Am I asking for trouble by specifying tankless for my clients?

David
DAVID BERGMAN ARCHITECT / FIRE & WATER LIGHTING + FURNITURE
architecture . interiors . ecodesign . lighting . furniture
bergman at cyberg.com    www.cyberg.com <http://www.cyberg.com/>  
241 Eldridge Street #3R, New York, NY 10002
t 212 475 3106    f 212 677 7291 

At 08:08 AM 11/17/2006, Lawrence Lile wrote:


	I've noticed that both of the tankless water heaters I've owned have problems regulating temperature at low flow.  (Bosch and Tagaki).  Some friends were sitting around complaining about this, (that's how popular the tankelss heaters are getting!) and one of them says he always suggests that Tankless owners will be happier with thier showers if they take out the flow restrictor in the shower head.  A little work with a pocket knife opened up the restriction in mine, and suddenly the shower quit wandering in temperature throughout the experience.  
	 
	I had hoped the new Tagaki was better about this, so I did a test.  At 1 GPM flow, the heater cycles on and off, and the water temperature wanders from cold to about 80F and back again every two minutes.  Pretty sad, actually.  
	 
	Of course coring out the flow restrictor uses more hot water, which uses more energy, and the point of the tankless water heater is to save energy.  The shower is just one component of the water system, this modification doesn't affect the dishwasher, kitchen sink, handwashing or clothes washing.  So maybe in the grand scheme of things it isn't that much of a sacrifice. 
	 
	The other situation that the low flow failings are annoying is hand washing dishes.  I'll often run a little hot water to wash a pot, shut it off, run a little more, and these short bursts of hot water use don't get the unit up to temp, they are just bursts of cold water.  In frustration I end up leaving the hot water running, at a fairly heavy flow, so it stays hot while I am handwashing.  Once again, using more hot water to compensate for the tankless unit's failings. 
	 
	I started looking into the idea of a very small electric tank unit in series.  Fed by the tankless, which does most of the heavy lifting, the tank would hold 5 gallons of hot water, and deal with short bursts of hot water use.  Presumably if you are using a lot of hot water, the tankless unit would catch up since it works well at higher flows.  So the small tank would mostly just have to compensate for it's own heat loss, would not have to heat much water from 52F.  I calculated the energy loss for such a tank as costing about $5 a year, if it doesn't have to heat any water, and that's before I wrap it.  
	 
	All of these modifications are taking me in the wrong direction, toward more energy use.  Has anyone else dealt with the low flow issue with a tankless heater?  How did you deal with it?  Or did you just tolerate it?
	 
	--Lawrence Lile
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