Solar Evac Tube question

Pat_35

That is 57 million btu's... for a month? I must be missing something. whew...

Wayco Wayne_2

I've been sneaking up

on my Solar project working on weekends and spare time. Figures when I finally get the system shipped my business got VERY busy. I'm not complaining. Last Summer I was slow, now that the economy is worse I'm busy. I'll take it. However.... I am close to charging my piping and installing my Evac Tubes. My question concerns installing the tubes. Someone here on the Wall said that they used a soapy water solution on the glass to help slide the tubes in the rubber grommets. (More cheeeese Grommet!!) Also they said that instead of using the thermal paste on the heat bulb they used "Never Seize." compound. I love the idea of using N.S. but wonder if it is a practical idea or if it has any drawbacks. Same with the soapy water solution. Good or no. WW

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Paul Pollets

Tubes

We simply make sure the tubes are clean when installing, and handle with clean cotton gloves. Don't want finger oils on the glass. I've never used any heat transfer compound on the copper element that inserts into the collector header.

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singh

Who's evac tubes?

The Viessmann tubes really don't need to be slid in, but rather pop open the header clamp and insert tubes.
I thought you were doing a drain back with flat panels?

Send pics, when you get everything going.

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hot_rod

the thermal paste

is critical fior the thermal exchange component. It serves as the final "connection" between that high temperature condensor bulb and the well assembly.

The evac tube is only as powerful as that final link allows when transferring the energy.

It is usually supplied with the kit. I'd use the product the send or suggest as it is more of a thermal paste than anti sieze formula. Why not us the correct stuff?


hr

rene_4

never sieze and liquid detergent.

I used the Never Seize. The supplier I purchased the tubes from recommended it. The condensing bulbs were real tight where they enter the manifold. I had to work each hole just to get each condensing bulb to slide in. The bulbs still fits very tight (metal to metal)and the never sieze is to prevent corrosion between the two dis-simmilar metals. The condensing bulbs are plated with nickel. No lubricant came with the tubes. I also used liquid detergent on the grommets. Worked real good. It would have been a bear without it.

Rene

Unknown

Lubricating seals

I tried the soap like Rene at first and I had the problem of the soap drying in the hot sun so I switched to silicon grease and cleaned the tubes with windex afterwards. Honeywell thermal grease is only 20 bucks and because the wells are very tight, unlike thermometer wells, very little is used. They do sell grease for mounting heat sinks on electronics loaded with silver or gold but it just isnt worth it.

hot_rod

think about the thermal expansion

and contraction taking place at that copper bulb. That copper tube will be at ambient conditions before the sun comes up, maybe well below zero this time of year.

Under full stagnation conditions that bulb can approach 700F. The transfer grease helps keep the "connection as the bulb expands and contracts.

You'll notice the tubes are much harder to slide in if they are in the sun. I've measured that bulb over 400F just before installing on a sunny day.

The grease, according to the manufactures should be checked and replaced after a period of time. it's a tough life working at those temperature extremes.

I've heard some talk about under-performing evac tube arrays. I suspect that bulb to well connection has something to do with it. I've installed some very loose fitting ones on some of the "price point" imports. Looking at the quality of the workmanship on the header and well fabrication, I can see why.

Lots, of technology, tolerances, seals and stuff with evac tubes.

Hard to beat a sheet of copper in a glass enclosure (flat panel collectors) for longevity and performance

hr

Unknown

I dont know Hot Rod

I reset my energy meter a couple of days ago,it was 7 degrees all day and I still collected 32000 btus. I dont think a flat panel will get that. And we had some really bad wind a week ago and I think flat panels at 55 degrees on my roof would have had a hard time.

Wayco Wayne_2

Singh!

I went to a solar conference in Annapolis, MD sponsored by my Solar Association for the MD, DC, and VA area. I learned stuff that changed my mind. I started using MS Virtual Earth to scope out my site from above and found my solar site was 45 degrees off true South towards the East. So I only get sun the first 2/3rds of the day in Winter. The tubes I chose have a round absorber plate in them so the plate is always facing the Sun when it is on the back side of the house. I imagined the flat plate would be reflecting the 45 degree angle off the glass and not absorbing much when the sun was south. I liked the drainback since it would let me oversize for Winter and then shut down when the temps were high in Summer. Now I have to build in a heat dump. Alittle extra material and time and the price of running a circulator to dump heat when I could be spending nothing on a drainback. Loto choices had to be made. I liked the ability to work alone and the lowere wind resistance of the tubes. I'm leaving the possibility of putting a flat plat in the system on the SW side of the house to catch the afternoon sun. We'll see how the 90 tube arrays work facing SE first. WW

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hot_rod

flat panels last week in Milwaukee

at 10F ambient, bright sun. We had a 120 gallon tank solar down to 39F by running the pump through the night.

By days end we had 121F in the tank.

Here are the performance numbers from the SRCC testing, here is the performance formula, defined by SRCC and we have the actual real life data.

We are running a 3 gpm flow through 3 panels, a bit higher than the .62 per panel that SRCC tested, so we do scrub a bit more than their numbers, as our actual data confirmed.

No need to guess which panel does what under what conditions. In fact at those conditions the flat panel will, IS, outperforming the evac tube, according to the test data compiled by the SRCC.

Certainly, as the graph indicates, as it falls below 10F outside, or you run a higher Ti the evac tubes will pass the flat panels.

It's all about the conditions at the panel Ta and the temperatures you are driving them to. In our example Ti of 110 - Ta of 10 divided by 300 for bright sunny conditions gets you to the number on the graph.

If you know, or assume the amount of radiation, ambient at the panel, and return, it is a simple math formula.

Included also is the RET Screen calc for Milwaukee across the year.

Also got to Bob's "solar is hot" website to watch tubes and panel running in real time. png 13 show what is happening in upstate NY as I post.

hr

Unknown

Hot Rod

What is the max temp you get from flat panels? I just sold a four panel system, I actually got a price drop in the flat panels that really makes them atractive.

hot_rod

winter months

I'll see 155F commonly in my area. Summer months 185F. That's with 2 gallons of storage per square foot of panel.

The 3 panel system in Milwaukee, with little to no load goes to 185F every sunny day. It goes into overheat protection mode, when the panel temperature hits 285F and over charges the tank.

The control allows the tank to go as high as 203F, just below relief valve setting (210). then they stagnate until the re-cool feature kicks in at night. We fired the system up for the first time in August. I suspect June and July will run right up to that limit, easily.

There should be plenty of temperature to run an absorption chiller for cooling.

The re-cool brings the tank down to 139F by morning.

hr

Pat_35

577 Therms...?

I have an evac tube customer who used 577 therms of NG to heat her house for 33 days. How many evac tubes would be needed at 200 BTU/hr per tube for that month? I am trying to find the formula... no luck---
Thanx

michael_34

therm to btu

one therm = 100,000 btu's.
: )

Unknown

Max temp should not be an issue in any case.

you can get high temp out of evac tubes, sure, but only at tiny flow rates.

usable heat still comes from the tank. That is mixed, and is determined by BTU collection more than anything else.

Flat plates can blow up a tank just as well as evac tubes can, so I don't think they are a limiting factor on what you can do for a tank temp.

Pat_35

Thermosyphon Systems...

Has anyone out there installed or use a Solar Thermosyphon heating system? Any overheating problems...?

EricAune

Nice data

Those are Solarskies panels made just miles from my shop in Minnesota, very nice! They do make some nice flat collectors.

Bob Gagnon plumbing and heating

Flat Panel Question

I am looking at a job, at a school, using flat panels. The school will have no summertime load, should I use drainback or are the lower maximum temps in a flat panel collector OK with the anti freeze?

Thanks, Bob Gagnon

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Mark Eatherton

Absolutely ,drain back, or

some means of rejection, which doesn't rally make sense.

Anti-freeze starts breaking down around 300 degrees F, if memory serves me correctly. Flat panels go to 350 plus degrees F during stagnation. It turns it into glycolic acid which then feasts on copper....

ME

Bob Gagnon plumbing and heating

Thanks Mark

I didn't know flat panels could get that hot, I think I'll go with drain back, I see enough rejection in my dating life.

Thanks, Bob Gagnon

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JJ_4

If I am right....

That means:

57 million BTU's/31 days/24 hrs = 77,553 btuh.

Pat_35

Drainback

Why are you using flat panels...? What is your Latitude?

Evac Tubes are more efficient and cost effective. Drainback is the way to go with 1/4" drop per lateral foot... is there any chance of freezing? Take a look at dogstarsolar.net

Unknown

Evacs aren't really performing any better according to those who measure things.. and I certainly wouldn't call them "cost effective" at twice the price.

Easier to get on a roof, yes. Easier to design for uber low-flow, high temp, yes. More heat in marginal collection periods, yes. But Flat plates are still very solid solar contenders.

Mark Eatherton

So Pat...

I see you are at altitude. Have you experienced tube failures at altitude yet? I know people that HAVE had a LOT of issues (25% failure rate) with the evac tube collectors, specifically the ones you deal in...

Just curious.

ME

JJ_4

Absorption Chiller - Solar Question

Hot Rod - What absorption chiller brands are out there that would be sized right for residential (3-5 tons)? All I seem to be able to find on-line are large units.

Thanks

Bob Gagnon plumbing and heating

My Flat Panel Collector

Outperforms my 120 evac tube array by a mile, I have lost 4 evac tubes in only four years, and have had no luck getting replacements. I think a good copper flat panel should last 50 years or more, if the anti-freeze is maintained.

Thanks, Bob Gagnon

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Ron Huber_2

Its' Friday Folks

Time for me to vent. This Dogstar solar outfit sounds like they just got in the business. They make unfounded claims and obviously listen to their reps B.S., solar works with both tubes and plates, apples to apples quality will give the plates the advantage in price and durability, performance per sq. ft. may lean towards tubes, but with more sq. ft. at less price point,plates win out, the only time we use tubes is when the site is off from south enough to warrant them (rotating them in the rack either way to compensate) or the customer just likes the looks of the tube system. I have tubes on my own house, wife liked the look better and would not let me do plates on the front of the house, she's the boss.

hot_rod

the numbers don't add

up that well. Their site mentions over $10,000.00 in fossil fuel savings for a family of 4 over a 9 year period?

My RET Screen examples show something between $360- 500 per year for a family of 4 with 80 gallons per day use. That is with fuel oil at $3.78 per gallon @ 80%, , electricity at .14/ kw @ 90%, and LP at 2.29 @ 65% efficiency. My numbers show about 1/2 of their claims??

hr

Pat_35

Evac Tubes---

Rob... Thanx for your response...

Well... Our Evac Tubes are SRCC rated... Are your Flat Panels rated? One 30 Sq Ft Evac Panel is rated for at least 8,600,000 BTU's per year by the SRCC. The only way to get the 30% tax credit is with SRCC units.

What is the rated BTU output of any flat panels made...? Flat panels have a reduced life span don't they? Quality Evac Tube panels are good for over 30 years with no degradation.

A good discussion...thanx---

Pat_35

tube failure...?

How can they fail...????
Thay have no mechanical arts...---

They work fine at 9,0000 feet and good for over 30 years.

The entire panels are warranted for 10 years and covered for any meteor strikes with your insurance. A 3/4 inch steel bearing dropped from 32 feet on horz evac tubes do not break them.

Where are you hearing problems....?

Pat_35

Some Evac Tubes are SRCC rated

No... we are not new in the business. Flats work great south of 35 degrees Lat. No so well North of that.

Well... Our Evac Tubes are SRCC rated... Are your Flat Panels rated? One 30 Sq Ft Evac Panel is rated for at least 8,600,000 BTU's per year by the SRCC. 42,000 BTU's per day. The only way to get the 30% tax credit is with SRCC units.

What is the rated BTU output of any flat panels made...? Quality Evac Tube panels are good for over 30 years with no degradation.

A good discussion...thanx---

Pat_35

Redo your RET Screen.

Pat_35

30 years...=$220,000

Over $10,000 saved in 12 years with about $500 per year saved. Over $200,000 saved in 30 years. Run it thru a savings calculator or RET screen with 14% saved per year with payback year of 4 or 5.

Dont forget inflation and fossil fuel increase. The numbers are good.

michael_34

577 therms equals 577,000 btu's

not 577 million. There is no multiplier there.

michael_34

Pat

michael_34

aahhhhhh,,,

Pat_35

Tube Replacements

I can send you 4 tubes. Who is the manufact?

We have been in the business a while and have plenty of tube stock laying around since they do not fail on their own.

michael_34

forget it!

Pat_35

no prob...

I can not remember what to forget.

Ron Huber_2

North

Have been installing flat plates for 32 years, here in Central New Hampshire at the foothills of the White Mountains, I think they work just fine here. Save $500 a year for 12 years, comes to $6,000. I think your calculator belongs with your rep for the tubes.