[Greenbuilding] [BULK] Tankless HW and hard water

[Lawrence Lile]

Here is a test at a lab that showed an alarming decrease in efficiency
in a head-to-head test of tankless and tank water heaters due to lime:

http://64.233.161.104/search?q=cache:QVTCjQdsMUgJ:www.pmengineer.com/CDA
/Archives/8cf9e86f7c298010VgnVCM100000f932a8c0____+lime+tankless+water+h
eater&hl=en&gl=us&ct=clnk&cd=1



" Testing showed that lime scale build-up is a major concern in hard
water areas with tankless water heaters. Lime scale did not flush out of
the heat exchanger from the water velocity through the coil, but
accumulated in a very short period of time. Lime scale can also
accumulate on the base of storage water heaters, but much more
gradually, making storage water heaters more tolerant of hard water
conditions. Adding a water softener on the water supply would prevent
the quick accumulation of scale on the heat exchanger. Tankless #2
started out with a higher efficiency rating, but dropped off for the
two-week period of operation due to scale buildup in the heat exchanger.
The efficiency rating could be up to two points higher using softened
water. Tankless #1 was less sensitive to scale build-up, but still lost
about 1.75% operating efficiency after a two-week period of hard water
conditions. Both tankless water heaters have a procedure to remove the
lime scale from the heat exchanger by flushing with vinegar using a
circulator. This requires at least one hour of service time, adding to
the life-cycle cost of the tankless water heaters in hard water areas.
To maintain peak efficiency, the tankless models must have water
conditions with less than 11 grains of hardness. The MI40T and M440T
models did not show a noticeable drop in efficiency during the test
program. "





-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Keith
Winston
Sent: Wednesday, September 06, 2006 12:43 PM
To: Greenbuilder list
Subject: Re: [Greenbuilding] [BULK] Tankless HW and hard water

It's not obvious to me why this would be so. Anyone care to share
thoughts? Lime formation won't tend to happen below, I think, about
160F. But surely in a tankless there are hot spots that exceed that? 
Maybe that's the answer right there? Or perhaps it doesn't form well in
a stainless steel environment...

Keith


Dr. C.F. Vasile wrote:
> Yes. I've been heating my house and water with a 15 kW Tankless 
> electric heater since 1996. I live in Patchogue, NY where cold water 
> temperatures drop below 45F in January. We have very hard water and 
> have had no problem with calcification. In contrast, the tankless coil

> in our obsolete oil burner used to "lime-up" in 6 months or so. When 
> it did, its 1.5 gallon per hour firing rate (oil) couldn't sustain a 
> low flow shower and its water-heating efficiency dropped below 25%.
>
> ----- Original Message -----
> From: "Lawrence Lile" <LLile at projsolco.com>
> To: "Greenbuilder list" <greenbuilding at listserv.repp.org>
> Sent: Wednesday, September 06, 2006 10:45 AM
> Subject: Re: [Greenbuilding] [BULK] Tankless HW and hard water
>
>