Solar Hot water panel questions

[jrd1990zr1]

Newbie just starting to layout a system. At 43 degrees latitute. Upstate NY so lots of winter snow.

I am considering installing evacuated tubes on a vertical wall 2nd story, facing due south. Could get about 12 LF on the wall. Also consider installing some flat plate collectors on the 4/12 pitch roof below the wall.

Any downside to mixing the types of collectors? Should the cold water enter the flat panels then tube header in series or separate loops?

Recomendations on best flat panel efficiency vs cost?

Best E-tubes efficiency vs cost?

Thanks in advance.

[Naptown]

They should be separate loops. Each time the water passes through another collector the efficiency of the collector down line goes down.
What is this to be used for hot water? heat ?
12" of tubes would be more than adequate for a residential hot water load ( about 50 tubes)
If it is for space heating I would recommend flat plates and a drain back if it is a fairly large array. This will alleviate some of the overheating problems that can arise in an oversized glycol system during the summer.

[LucMan]

If you want to use the vertical wall you will need to use U tube EV tubes at 90 degrees. Heat pipe EV tubes are not recommended for vertical mounting. Do you have an overhang above the vertical wall that would shade the array in summer?

I Like AET flat plates with a drain back tank for all around performance.

[jrd1990zr1]

They should be separate loops. Each time the water passes through another collector the efficiency of the collector down line goes down.
What is this to be used for hot water? heat ?
12" of tubes would be more than adequate for a residential hot water load ( about 50 tubes)
If it is for space heating I would recommend flat plates and a drain back if it is a fairly large array. This will alleviate some of the overheating problems that can arise in an oversized glycol system during the summer.

I was thinking of using the tubes on the vertical wall for domestic hot water and see how it goes. This time of year the wall gets almost a full day of sunlight. There is some minor shading in summer.

The flat plates on the 4/12 roof would be a second phase for supplemental heat in the winter. I have an area in my basement (poured concrete) with three sides which would make a good large water mass storage tank (could be as large as 2000 gallons). I figured if I had too much domestic HW in the primary system I could use the storage agea for a "heat dump".

Thanks for the advice.

[jrd1990zr1]

If you want to use the vertical wall you will need to use U tube EV tubes at 90 degrees. Heat pipe EV tubes are not recommended for vertical mounting. Do you have an overhang above the vertical wall that would shade the array in summer?

I Like AET flat plates with a drain back tank for all around performance.

I am not familar with "U tube EV tubes", can you elaborate? I spoke with a local person with a very large array of vertical tubes and he claims they were not a problem. Can you direct me to more information on this?

Thanks

[russ]

The two types of evacuated tube collectors that I am aware of are:

1) The water never enters the evacuated tube - there is a heat pipe inside the vacuum that carries the heat to the header. The heat pipe is filled with a solution (methanol I believe) that refluxes up and down inside the heat pipe.

2) Water actually flows inside the evacuated tube from the header and then returns to the header. With this type there is much more of a problem with leaks and the vacuum seal from what I read.

Type 1 is the most common.

With either type a heat exchanger is needed - the water to be consumed should never enter the collector or header.

Russ

[jrd1990zr1]

The two types of evacuated tube collectors that I am aware of are:

1) The water never enters the evacuated tube - there is a heat pipe inside the vacuum that carries the heat to the header. The heat pipe is filled with a solution (methanol I believe) that refluxes up and down inside the heat pipe.

2) Water actually flows inside the evacuated tube from the header and then returns to the header. With this type there is much more of a problem with leaks and the vacuum seal from what I read.

Type 1 is the most common.

With either type a heat exchanger is needed - the water to be consumed should never enter the collector or header.

Russ

Thanks Russ.

Are you aware of any problems having the type 1 you described mounted on a vertical wall? I am not aware of the situation LucMan described in his post.

Thanks, John

[russ]

Hi John, I don't know. Possibly it is due to the way a heat pipe functions. I expect it would be more efficient when inclined so the fluid runs down the tube wall and picks up heat.

My guess - In the vertical plane there would be less contact between the fluid and the tube wall meaning great heat transfer at the bottom of the tube and between none and poor for the higher portions of the heat pipe.

Quite possibly (if I am right) not much inclination would be required.

Russ

[Naptown]

We use Apricus tubes good value for the money. They will need to be angled slightly from the wall which is accomplished with the racks that come with it.
I would size the tube array for the hot water load you expect to have. Generally here in Maryland about 10 tube per person and about 1.5 gallon of storage per tube. Properly sized for the anticipated load will prevent overheating.
For the space heating you really want to pitch your collectors up to about latitude + 15 degrees. Laying flat on 4/12 roof won't give you much heat in the winter and bake in the summer.

[russ]

I like the Apricus website - one of the better ones I have seen for evacuated tubes. Lots of good information!

I was at a solar fair here and talked to a sales company selling evacuated tube collectors. When I got home I was looking at their website and found it to be a copy of Apricus to a great extent. I asked them about it and they said they were not selling Apricus collectors and Apricus must have copied their site. I just laughed and tore up the local companies business card.

I was really hoping they were selling Apricus but no luck. Apricus does (did) not have any reps in Turkey - I emailed them to find out.

Russ

[Naptown]

The thing I really like about the Apricus is the tubes are modular in their construction. There are really 2 things that go wrong in a tube. Generally and top of the list is loss of vacuum. Secondly the heat pipe goes bad.
With Sunda and Thermomax The vacuum is held by rubber seals. Generally the most common failure. Apricus is a double wall welded glass enclosure with a low e coating between the walls.
Heat pipes, absorber, glass tube can be disassembled in the field for replacement if necessary and all parts can be purchased separately ( good for the rock from the neighbor's kid or lawnmower)
Warranty is also longer than others.
Oh and priced very well also.

[LucMan]

I am not familar with "U tube EV tubes", can you elaborate? I spoke with a local person with a very large array of vertical tubes and he claims they were not a problem. Can you direct me to more information on this?

Thanks

Here you go.

http://www.sunmaxxsolar.com/evacuated-tube-solar-collectors.php

http://www.sunmaxxsolar.com/heat-pipe-vs-u-pipe-solar-collectors.php

EV Heat pipes have a small amount of water & alcohol in the bottom that when heated turns to steam and rises to the top where the heat is transferred into water in the manifold. The steam condenses and turns back to water and falls back to the bottom to be reheated. If the tubes are vertical the condensate and steam could come in contact with each other in way that could cause steam hammer. ( not good for fragile glass). If you have ever experienced a steam heating system you will know what I am talking about. That loud clanking, banging, pipe shaking sound that comes from steam blowing by condensate in a radiator or piping system. This would quickly destroy an EV tube system. The simple fix for a steam heating system is to tilt the radiator towards the valve to allow the condensate to run out faster. Same story with heat pipe EV tubes, they must be tilted, I think the min. is 15- 20 degrees from vertical

[jrd1990zr1]

Here you go.

http://www.sunmaxxsolar.com/evacuated-tube-solar-collectors.php

http://www.sunmaxxsolar.com/heat-pipe-vs-u-pipe-solar-collectors.php

EV Heat pipes have a small amount of water & alcohol in the bottom that when heated turns to steam and rises to the top where the heat is transferred into water in the manifold. The steam condenses and turns back to water and falls back to the bottom to be reheated. If the tubes are vertical the condensate and steam could come in contact with each other in way that could cause steam hammer. ( not good for fragile glass). If you have ever experienced a steam heating system you will know what I am talking about. That loud clanking, banging, pipe shaking sound that comes from steam blowing by condensate in a radiator or piping system. This would quickly destroy an EV tube system. The simple fix for a steam heating system is to tilt the radiator towards the valve to allow the condensate to run out faster. Same story with heat pipe EV tubes, they must be tilted, I think the min. is 15- 20 degrees from vertical

LucMan

Thank you for the information. The distributor is only about 1.5 hours southwest of me so maybe a field trip is in order. I may be able to live with 20 degrees from vertical.

Thanks again, John

[russ]

I can't see how you get steam hammer where there is no flow - the flow is what causes the hammer.

Generally the type where the water enters the tube (as compared to using a heat pipe) are considered much more of a problem.

The Apricus web site is quite good www.apricus.com

[LucMan]

LucMan

Thank you for the information. The distributor is only about 1.5 hours southwest of me so maybe a field trip is in order. I may be able to live with 20 degrees from vertical.

Thanks again, John

Where in NY are you?
If you are in the Adirondacks check that the heat pipes are rated for -30F. Some of the brands heat pipes were freezing & bursting in extreme cold. I know someone that lives on Lake Winipeg that had his freeze, the company covered the replacements under warranty with the lower temp rated HP. The replacement pipes had a thicker wall and had alcohol added.