Heating Help

Recirculation heat loss data

@ April 26, 2012 7:05 AM in direct system

Attached are plots from the nights of Apr 17-18 and Apr 24-25. On the night of the 24th, I put the pump on a timer which cycled the collector pump for 3 minutes on the hour starting at 10pm to 7am. There is zero load. Apr 17-18 is just standby losses, with no pump cycling until 6am where it cycled once since the collector hit 40F.

With the tank at 140-160, the tank will lose around 0.8F per hour strictly standby losses.
With the tank at 160F, and a three minute collector pump cycle per hour, the losses increase to about 1.8F per hour.

The overnight temperature swing was about the same both nights, from 65F down to 40F

Availability

@ April 25, 2012 11:19 AM in A. O. Smith Cyclone Xi Field Performance

You make a very good point that explains why the uptake of innovation can be slow.

No one replaces their water heater unless it is an emergency.  When that happens, they are forced to use something that is in stock in town.  They just can't wait 2 weeks, period.

So the only way these heaters will gain market share is:
1.  Convince property managers that they will save money and (maybe) last longer.
2.   Convince someone to prepurchase a few to have in stock.

Two anode rods

@ April 25, 2012 10:11 AM in A. O. Smith Cyclone Xi Field Performance

I think that having two anode rods and the fact that sediment and loose scale don't cause problems could definitely increase the life expectancy of this tank.

96% efficiency is a big bonus too.

I agree

@ April 23, 2012 11:15 AM in expansion tanks on DHW systems

The other issue with the toilet valve pressure relief is that when it fails, nobody will bother tracking down the correct replacement valve, and then the water heater will have the same problem.

Heat Flo Indirect tanks

@ April 23, 2012 11:09 AM in Domestic Water System Design Contest- Win $100!!!

Dave,

Thanks for turning me on to Heat Flo indirect tanks. Although I've seen stainless tanks fail prematurely in the past (Glowcore) I believe in their potential to outlive glass lined steel tanks. HF is very reasonably priced: http://www.houseneeds.com/shop/heatflo/heatflostoragetankbuy.asp

The warranty doesn't fall in line with this hope, though. HF gives you 5 years, but the AO Smith Cyclone has a ten year warranty. It seems like the ten year tanks all have TWO anode rods. Can I get 20 years lifetime if I replace the rods? (That might be another thread)

Cost Discussion

@ April 23, 2012 10:49 AM in Domestic Water System Design Contest- Win $100!!!

Mark,

I think that is a great strategy, I just have to spend some time comparing the cost vs. savings.

Threads like this one are tough when cost discussion is disallowed by the forum rules.

A. O. Smith Cyclone Xi Field Performance

@ April 22, 2012 1:22 PM in A. O. Smith Cyclone Xi Field Performance

I'm looking for any feedback, good or bad, on this water heater:
http://www.wallingfordsales.com/proddetail.asp?prod=42289&cat=47

It's for a small apartment building, and seems almost too good to be true.

A. O. Smith Cyclone Xi

@ April 22, 2012 1:19 PM in Domestic Water System Design Contest- Win $100!!!

This water heater has apparently been around since 2007.

It is 95% efficient for the same price as an old style natural draft .60 EF heater.

http://www.wallingfordsales.com/proddetail.asp?prod=42289&cat=47

Toilet Valve can also solve the problem

@ April 21, 2012 11:02 AM in expansion tanks on DHW systems

In researching this issue, I discovered this toilet valve:
http://www.watts.com/pages/_products_details.asp?pid=7237

When the water in the tank expands, this guy will just dump a little down the drain at 80 psi, say, instead of the 150psi setting of the T & P relief valve that is on the tank. In new construction, this saves a little money.

When Denver suddenly required backflow preventers in multifamily buildings, all my water heaters started failing. Duh. The pressure swing from 60 to 150 psi a couple times a day did them in pretty fast. I think it causes a crack in the porcelain glass coating on the inside of the tank, and the unprotected steel tank rusts out in about 3 years.

Just another one of the many unintended consequences of code requirements.

Condensing tank is an good choice

@ April 21, 2012 3:51 AM in Domestic Water System Design Contest- Win $100!!!

And AO Smith has the best selection.
Henry, you are definitely in the lead for the contest.

It's not worth risking Legionella, so I'll turn it up to 131F if Wikipedia can be believed:
"At 55 °C (131 °F): They die within 5 to 6 hours
Above 50 °C (122 °F): They can survive but do not multiply"

They do make a 120 gallon residential electric water heater: http://www.pexsupply.com/Bradford-White-M-2-120R6DS-120-Gallon-Energy-Saver-Electric-Residential-Water-Heater

But the AO Smith would be more cost effective .

Legionella?

@ April 20, 2012 8:01 PM in Domestic Water System Design Contest- Win $100!!!

Since the water heater turns over at least twice a day, I didn't think Legionella would be an issue. I thought the water had to stagnate for a little while. In a 20 unit building, the longest stagnation period is about 6 hours.

dp

@ April 18, 2012 9:29 PM in direct system

The Articles Ignore Steamback

@ April 18, 2012 9:29 PM in direct system

Part 2 of the above articles talk about stagnation and overtemperature protection in a closed system or direct system. They don't mention the best and simplest method, which is steamback: http://www.heatinghelp.com/forum-thread/133064/Steamback-System-Design

15 gpm isn't necessary

@ April 18, 2012 4:57 PM in Domestic Water System Design Contest- Win $100!!!

"You won't find a system that can deliver at least 15gpm-20gpm of DHW at 120 degrees for under $5K" I agree, Paul, but that's not what I need.

A gpm rating is not applicable to a tank style water heater. Gallons per hour is really more important. I currently have a 75gallon/75,000btuh heater installed. It has a 105 GPH rating (50F to 110F), and I haven't had a complaint in six years. It has 1" tappings.

I realize that there are plumbing codes that dictate the hot water flow requirements in a 20 unit apartment building. But in a replacement situation, I don't believe a plumber would get in any trouble by installing a heater that was matched more closely to the actual load than a worst case code requirement.

I also realize that most plumbers like to minimize the possibility of a callback. That's understandable, but for my building I'd prefer equipment that just barely satisfies the load at the lowest life-cycle cost.

All the showerheads are 1.6 gpm. Even for the morning rush, 105GPH is apparently enough. So that's really only 53,000 btuh at 100% efficiency.

Condensing with Indirect tank

@ April 18, 2012 10:36 AM in Domestic Water System Design Contest- Win $100!!!

A good condensing boiler heating a tank with an immersed heat exchanger would last a long time and be very efficient.

The cost would probably be 5 figures though.

So I'm looking for a strategy to reduce the installed cost. Maybe using a 120 gallon residential electric water heater as buffer/storage somehow could reduce the materials cost.

Domestic Water System Design Contest- Win $100!!!

@ April 16, 2012 4:00 PM in Domestic Water System Design Contest- Win $100!!!

I have a few 20 unit apartment buildings where the sidearms were removed years ago.
The commercial tank-syle water heaters don't last very long, and their EF rating is only about 0.60.

So I'm looking for a new approach. The cost should be in the low to mid four figures.
If you have a great idea, make sure your email address is available so I can send you a check. The right design will save at least $300/year per building, so I feel guilty asking for ideas without a offering a reward. (and it might make the brainstorming more robust).

I'm not afraid of using "residential" or Home Depot equipment if you think it will hold up in this application. It should last at least 12-20 years.

3/4" pipe and fittings are OK if they are kept to a minumum. The main lines are mostly 1", but there are never more than 3 showers going at the same time.

The current gas usage for DHW, which should drop, is about 10 therms per unit per month. I should stay with natural gas, so no heat pumps.

The space heating system isn't ready to upgrade yet, so no combination systems. It should stand alone. I can upgrade the flue if I have to.

Expected reliability is just as important as first cost. Maintenance costs should be estimated. Extra points for high efficiency without extra maintenance. It's Denver Water, so water quality is not an issue.

Getting some cool nights this week

@ April 13, 2012 1:52 PM in direct system

Karl,

Most of my data so far was taken with our random daily usage thrown in the mix.

That makes it tough to tease out much meaningful info.

So I've isolated the solar system (zero load, only ambient and recirculation losses) for the next few days. We should then be able to compare a hot tank with and without recirc. losses. I think that's our big question.

My collector loop uses high pressure EPDM hose insulated with 3/4" armaflex. More info & photos to come.

I'm presenting these results at the WREF on May 14: http://ases.org/conference/
"FORUM -
Advancements in RE Technology: Radically Reducing the Cost of Solar Water Heaters - 5/14/2012 4:15pm - 5:30pm"

Hasn't been very cold since mid Feb.

@ April 12, 2012 11:38 PM in direct system

When the tank is at 160F, I lose 10F overnight without any pump cycling.

When the pump cycles, the increased heat loss is under 4%.

Cycling at night

@ April 12, 2012 10:07 AM in direct system

Here's a couple plots of my collector return temperature.

On pretty cold nights (15F), the pump cycles eight times.

Draindown vs glycol vs drainback vs recirculation

@ April 11, 2012 12:33 PM in direct system

It all comes down to a pretty simple failure mode analysis problem.

All four strategies have several failure modes. Consider this analogy: Gas boilers have many complex failure modes but through the years all of them have been solved. And all the while costs have come down. Their current failure rate is negligible.

By comparison, ET collectors, with freeze tolerant collector loop piping and redundant controls is a dead easy problem for good design engineers.

Installed system cost is currently the biggest problem for the SDHW market. Since recirculation is the cheapest system design, it starts becoming obvious that whoever can drive down its failure rate may have a winner. Ritter and Resol already claim to have done it, and continue to gain market share due to cost.

Not a trivial topic, the potential US market is 252 billion

"Boiling it Down"

@ April 10, 2012 5:44 PM in direct system

Here's the passage in the magazine articles that jumps out at me as "new stuff":

"Evacuated tube collectors,
by their very design, do not contain any water
in the absorber, and the absorber itself can
freeze without any damage to the collector.
The water in the header piping is subject to
freezing temperatures, but it is enclosed completely
by insulation. While heat loss from a
flat panel collector is significant in freezing
conditions, heat loss from evacuated tube collectors
is nearly zero in the exposed tubes and
minimal (200–500 British thermal units per
hour) in the header. This means that the engineer
now has a third option besides glycol
and drainback: circulation of water during
freeze conditions, or a direct water system
(see Figure 3).
Using direct water in the solar loop obviates
all of the issues described above for
glycol and drainback systems. The engineer
must be concerned with only two issues:
scaling and ensuring circulation during
freeze conditions. Both of these are easily
addressed."

I wouldn't say "easily addressed", but here's some more of what I've learned:

1. Ritter, the German solar company that employs recirculation freeze protection in cold climates, is currently wrestling with some code officials and OG-300 requirements. The main issue is how big of a battery backup for the pump is required to prevent freezing? http://www.cpuc.ca.gov/NR/rdonlyres/22FFF2E8-20FD-4F50-BD46-B88921387972/0/LibreEnergyProtest.pdf

2. Ritter actually employs a brazed flat plate heat exchanger in their systems to prevent scaling in the collectors. Ironically, therefore, theirs is not a direct system. They use water in a conventional closed system for the collector loop, and rely on steamback for stagnation protection. (Which, surprisingly, was overlooked in the ASPE magazine article).

3. Ritter touts recirculation as also solving one more (rather rare) failure mode of glycol systems: On an extremely cold morning, a glycol collector loop will have a significant amount of sub-freezing fluid in it. When the collectors reach the proper temperature, the collector pump will kick on. The still-freezing glycol in the collector loop can instantly freeze the domestic side of a flat plate heat exchanger and and ruin it.

Don't dismiss Ritter (even though, yes, it's the candy bar company). They own 75% of the ET collector market in Germany and 35% in Europe. ETs are about 10% of the solar thermal market. They have begun to address the US market, but so far, only for commercial.

How About a Direct Split Self-Freeze-Protected Thermosiphon?

@ April 10, 2012 4:58 PM in direct system

Karl,

Wow! This strategy is my current obsession.

The seminal paper on what you are talking about is here: http://www.thermomax.com/Downloads/Reciculation.pdf

It proved that the heat lost by an evacuated tube (ET) collector loop is negligible at night. Therefore, recirculation freeze protection is back in play for cold climates. This is old news in Germany: http://www.ritter-xl-solar.com/en/technology/water/

I've tested this through two Denver winters and learned a few things, mainly that it does work!

For the ultimate in system simplicity and low cost, you can eliminate the pump and controller if the house is configured correctly (south facing wall) as in this video:
http://www.youtube.com/watch?v=Q5rKLsJl3cY

Other strategies can be employed that involve pumps if the collectors are higher than the tank.