Solar Customer

Unknown

why a second tank instead of an on demand backup HR?

Paul MacDougall

Solar Thermal Customer

Have a customer interested in Solar DHW. Gave him a quote for a Buderus system. Now he would like a quote for Solar DHW for his house on Flat Panels, Solar DHW for one outdoor shower on Evac tubes, and Solar space heating for one radiant panel. He currently uses an oil fired (using B50) steam boiler with tankless and a storage tank. He wants to be as green as possible, but more importantly he wants everyone in the town to know how green he is being. If money wasnt an object I would just go along for the ride but it is. ALso I think he will burn more oil just to heat one radiator. I want to install one simple system, but I dont want to lose the job because I cant give him what he wants. Which direction should I go with this and any suggestions with equipment.

hot_rod

all doable

just one panel radiator on the solar? If it is just a "token" solar powered zone, use a solar control with two outputs. After it does the DHW load it would swich any remaining energy to the panel radiator.

You could use a dual coil solar tank for that, bottom coil for solar input, top feeds the panel rad.

No need to connect that one rad to the boiler. Some rads have the ability to add an electric element to the hydronic radiator. That could be the backup.

Depending on where you are located, how many solar collectors, the size of the storage, how much DHW they actually use per day, etc... you may not have a lot of excess energy to send to the rad, especially in winter months.

It sounds like a "show and tell" solar powered rad. Nothing wrong with that if he has the $$ to get it.

Just be realistic, and honest with him, on the reality of how much energy he will get from the system.

Use RET Screen or any of the solar design softwares to run various "what if" cases, adjusting collector size, tank size, etc. You could propose a couple options with some number crunching on the software. Customers like to see you have done some design homework, not just a shot from the hip.

hr

Paul MacDougall

Lets just say that I use a dual coil tank, using the top coil to heat one radiator. I would have to provide for a fill, purge, and expansion. I would also be drawing heat from my DHW, dropping the temperature of the tank causing the boiler to fire when the Solar couldn't do it, like cold winter nights. 1) Wouldnt this cause the boiler to run more than necessary for DHW? and 2) Could I use a three-way diverter to direct flow towards the radiator when the customer wants it and its available. Like a switch? Thank you for your suggestions, they are good ones

Paul MacDougall

Speaking of Retscreen, where do I find information on the
FR (tau alpha) Coeffecicient and FR UL coefficient variables.

hot_rod

Go to www.srcc

and select the panel you have or are planning on. That is where you find data specific to your panel.

Often the panel is in the RET Screen data base, use the program defaults if that is the case.

If for some reason your panels do not have the SRCC OG-100 listing, you will have to get the data from the manufacturer.

hr

hot_rod

yes

but the extra BTUs have to come from somewhere to run the radiator. You could use a 3 way diverter on the solar loop and switch to the radiator when the tank is satisfied. The radiator will have glycol in it, however. But once the sun goes down you have no stored heat to pull from.

If you pull heat from the top coil the tank temperature will eventually drop and the boiler will fire, if the radiator is calling for heat. Then the boiler has some "buffer" capacity (the solar tank) to keep it from short cycling which is what it may do with only one radiator connected directly to the boiler.

That's why I thought for a small radiator load, maybe electric back up would be a good method.

It all depends on how, and how much you want the solar to contribute to either load.

Ideally every morning you have a cold solar tank to get the most energy from the sun. But you will always need a backup for no sun days.

I prefer the dual tank setup. A dedicated tank for the solar, this feeds into the normal HW tank, or tankless, or whatever the DHW source is.

There are a bunch of ways to accomplish this, just depends on your goals. and budget

hr

hot_rod

dual tanks, or

an instantanous. I'm not sure anyone manufacturers one that can take warm, or hot feed and still operate correctly. seems we have seen a handful of posters here claiming the "solar" models they trued did not work as indicated??

I'd like to try a bunch of the brands to get some first hand experience. Feed them with 100,- 115F or so see how the perform.

Dual tanks do give you that dump load if they use a large tub and high GPM filler spout. It really depends on the customer as far as which is the best method. they all have pros and cons.

hr

Unknown

that's fair. we have been specifying electric on demands to end-run around the "boost" issue. I wonder if the Navien or the eternal hybrid unit there might do better, with their small actual mass in the unit. I'd like to see that sort of study done too... know any good grant writers?

Paul MacDougall

So if I were to set him up with one 80 gal dual coil Tank, I could use an existing 40 gal storage tank for space heating, by utilizing the second coil to bring my tank up to temperature, then pump it towards my radiator. While using the oil fired boiler with tankless to heat the whole setup when I must. So as of now I am counting 4 pumps, two aquastats, 1 differential control, and 120 gallons of water. I only mention the existing storage tank because the customer seems to really want to fit it into the system. But I can drop it if necessary.

Am I missing anything? I think I have already over thought this, and every manufacturer seminar I have been to has said not to do that.

hot_rod

most of the solar

controls have multiple outputs including delta T and or thermostat function. One control may be able to handle several of those functions and pumps.

Shop around and look at the "arrangements" the control offers. Several solar controls available have 3 outputs in a fairly simple and inexpensive control. Most have data logging functions to keep track of how well the system is actually performing.

hr

nathan_8

srcc address

The web address for the SRCC is:

http://www.solar-rating.org/

Wayco Wayne_2

My system

uses a 120 gallon storage tank with an upper and a lower HX. The return line to the boiler runs through the upper HX and draws heat for a radiant floor and a hydro-coil. If it's not hot enough the boiler kicks on and heats up the supply pipes. During the day I have the boiler turned off on a timer so the solar can contribute as much as possible. This method does not prioritize domestic hot water, but the trade off is while using the solar heated hot water for heat during the day it keeps the tank temperature lower so I can get better heat transfer in the collectors by having a larger temperature differential, thereby increasing my performance and harvest. In the Summer I got plenty of domestic for showers.

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Paul MacDougall

Wayne, did you add an array to accommodate for your space heating demand?

Wayco Wayne_2

Yes I added 2 arays

and have 90 tubes in total. I stood them up at 60 degrees so they would have a more direct solar path in Winter and not as much in the Summer. I have my snow melt sidewalk set to turn on when the storage tank gets up to 170 to shed heat. As far as I know it has never needed to come on. I've seen my storage tank as high as 165. It's been rainy here in MD so I havent had many long sunny days. Also My 2 girls moved back home because of the economy and take long showers and baths so my solar thermal is saving me a lot.

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