[Greenbuilding] Water heater timer energy savings?

John Straube jfstraube at gmail.com
Sun Apr 10 19:56:38 CDT 2016


Doubling the R-value cuts heat loss in half. That is not splitting hairs.  

 

You cannot feel the temperature of a tank and declare that there is no heat
loss.  By the same token, touching the outside of a house during cold
weather would tell you that it is not worth insulating a house with R-12. Or
maybe you are advocating that.

 

Yes, there is heat loss through components other than the tank, eg the
pipes, but that heat loss does nothing to influence the size of the heat
loss through the tank wall. It is additive.

 

I find it astounding that we are actually talking about insulation and heat
loss as if it is some hard to understand thing. Fourier would be spinning in
his grave.  The science is clear.  If your observations don't follow the
laws of physics, you must be missing something. 

 

Nick's numbers suggest that the savings would be only 0.28 kWh/day, and I
think that is a good estimate. That is a 100 kWh/yr, or around 2.5% of the
typical energy used by the average family on water heating.  I would find it
really hard to believe that anyone could measure this saving in an operating
household.  But this kind of saving would add up to several power plants if
widely deployed.

 

 

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org]
On Behalf Of Antonioli Dan
Sent: April 10, 2016 18:48
To: Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Water heater timer energy savings?

 

John, 

 

My comments below. 

 

 

 

On Apr 10, 2016, at 7:11 AM, John Straube <jfstraube at uwaterloo.ca
<mailto:jfstraube at uwaterloo.ca> > wrote:





Dan

The loss equation is

Heat Flow = Area * Temperature / R-value

So, the statement that there are diminishing returns is absolutely true

But the claim that you wont get energy savings is flatly, provable,
unquestionable false.

 

If we're splitting hairs then, yes, you can get "energy savings" by
investing in larger and more robust insulation, but the previous statement
that doubling the insulation of a hot water heater would cut its heat loss
in half is not true. Touch the side of any modern hot water heater and see
if you can feel any heat. You won't, so the insulation blanket won't really
accomplish much for a new hot water heater. Yes, it will do something.but
what that something is won't be determined by calculations, which is why I
prefer real-time, site specific measurement..which leads me back to see if
there is an integrated digital timer/meter instead of having to install two
separate units. 

 

 

Going for 16" of cellulose insulation to 32" of cellulose insulation will
cut heat flow through the ceiling in half.

 

I don't have time to dig up the stats to show that at least some research
claims this is not true. Energy upgrade incentives won't cover the cost of
an additional 16" of cellulose when the first 16" does most of the work.
Even in progressive cities like Berkeley where they have aggressive climate
change goals, they will not pay for that additional 16". 

 





Now it is entirely valid to ask, is that reduction worth the cost, the
hassle, the environmental investment.  But making such decisions with the
false belief that it does not save energy results in bad decisions.

 

And it's equally bad to assume that "more is good." 

 

Remember, buildings could care a less if they're insulated. And in fact,
they last longer and are more durable if they aren't insulated. It's the
biological species inside the building that wants the insulation, not the
building. 

 

 





 

How does this apply to hotwater heaters?

A top of the line water heater will have insulation of 2" of foam which in
service performs at maybe R14, likely less.  The old fiberglass insulated
tanks might have been insulated to as little as R-5, but many where
insulated to R-8 or so.

Adding R-10 any of these tanks will significantly reduce the heat lost on
standby. By over half for an old tank but by about a quarter even in a new
best in class tank.

As noted, the heat loss through piping is significant, so ensuring that
there is a loop to avoid thermosiphoning and some insulation along pipes is
definitely important before going beyond standard modern quality tanks.

 

 

The biggest heat loss for a modern hot water heater is through the
uninsulated pipes, and you'll get a much bigger bang for the buck if you
insulated the entire hot water lines (as required by many green
certification systems). 

 

When I directed a home energy upgrade program several years ago we energy
upgraded dozens of old homes and only a few had hot water heaters old enough
to justify installing an insulation jacket. And if you've ever installed one
you'll see why they don't work as well as they're claimed to. Under ideal
laboratory conditions where so many variables are controlled you can show
some improvements, but not a lot. Again, the next time you see a hot water
heater put your hand on the side of it and see if you can feel any heat. You
won't. The side will be cold and 98% of the "blanket" covers that cold
surface. The hot and cold lines on top will be warm, so that's where you
want to insulate. 

 

And all of this aside, investing in solar thermal is the best overall
strategy for reducing hot water energy waste. I'd rather put the time and
energy into a net-zero energy hot water system with monitoring and measuring
than splitting hairs on redundant insulation. Then gain, I'm an energy geek
like just about everyone else in here so don't be surprised if you see me
installing a hot water jacket.or two, or three...

 

Dan

 

 

 

 





 

 

From: Greenbuilding [
<mailto:greenbuilding-bounces at lists.bioenergylists.org>
mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of
Antonioli Dan
Sent: April 9, 2016 22:11
To: Green Building < <mailto:greenbuilding at lists.bioenergylists.org>
greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Water heater timer energy savings?

 

There's only so much insulation value you can get per application. I don't
have the "calories" per calculation, but insulation has its diminishing
returns. 14-16" of ceiling insulation is about all you're going to get from
that application..some people think that if you keep going up into 2-3 feet
that you'll get more energy savings and it's not true. That said I won't
want to go down an insulation rabbit hole. The post, once again, is about
digital timers and integrated watt meters. If you want to start another
discussion about insulation please do. 

 

Dan

 

 

 

 

On Apr 9, 2016, at 6:48 PM, Reuben Deumling < <mailto:9watts at gmail.com>
9watts at gmail.com> wrote:






 

 

On Sat, Apr 9, 2016 at 5:12 PM, Antonioli Dan <
<mailto:solardan26 at gmail.com> solardan26 at gmail.com> wrote:

Most modern hot water heaters do not need blankets as they are redundant,
and redundant insulation doesn't do much. 

 

Hm.

I'm looking forward to Rob Tom's response to that.

As for me, I'm not so sure about that. I can well imagine that some modern
water heaters are better insulated (but probably not as efficient as some
older designs), but how can adding more insulation with a payback of 1 year
or even five years be redundant? I can't imagine that the embodied energy in
a bit of fiberglass (or recycled jeans) would tip the scales.

 

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