Multiple Small Pumps vs Single Large (Help!)

Hello-

You might look into ECM pumps. They are AC but extremely frugal on power consumption. Look at Grundfos Alpha and Wilo (vee-low)
Stratos.

But first things first, do you have an accurate heat loss calculation? With the amount of money involved and comfort being the goal, you really need some solid numbers to figure out flow rates, supply water temps, etc.

Also, it might really be worth it for you to hire some design consultation(think Heaterman). Just to make sure you are not missing anything that's going to cost you more time and money later, not to mention the aggravation.

Good luck with your install,
Noah

You can run 4 separate pumps all hooked to one line (1 1/4", 1 1/2"?) or hooked to their own 1" pex line. One line would be preferred, (less heat loss, friction, plumbing complexity). You might find that bigger diameter pex is so expensive that separate 1" lines are cheaper than one larger line, otherwise I don't see any reason to consider separate lines. Ideally you'd have the largest possible single line, check valves on the additional pumps (one running 24/7 doesn't need a check valve) and a way to turn on only as many pumps as you need to meet your demand. One heat exchanger is better than multiple smaller ones in this instance, reducing the flow through a large heat exchanger might reduce turbulence and heat transfer, but I'm guessing that it will still be far more efficient than having idle heat exchangers.

Also, what is the 10 feet of head based off of? Is that mostly the heat exchanger? or just the lines between the garn and house? In either case, it may be cheaper to lower that power requirement (bigger piping, HX) than to meet it 24/7 for the life of the system.

Note that if you do use a single line with multiple small pumps the correct way to plump them is in parallel with check valves after each pump as opposed to series plumbing which will only increase head, not flow.

As stated, plumb multiple pumps in parallel in your case. That is assuming an El Sid can pump much against that head. You already shot yourself in the foot getting a Garn. Garn represents everything Americans DON'T know about burning wood. Have fun trying to run that half horse blower on panels. Half horse motors are great - for pulling stumps and pumping water over mountain ranges. Maybe you can sell it and recoup some of your costs. Nothing will break you faster than trying to run that beast. Please tell me you didn't get a plate exchanger, if so, try to sell it too. Look at Liang or Caleffi Solar circulators. They are the highest flow & head DC pumps I am aware of. You will want to look into a transformer to drive these pumps if they will see voltages over ~25VDC from the panels as they will shut down on over voltage to protect themselves - See Solar Converters Inc. for this. Forgive the other other posters, they don't live off grid and don't know a Liang/Caleffi/ElSid uses half the juice even a miserly Wilo uses and half again since you won't need the inverter going to run a Wilo/Grundfos/any AC pump. Nothing exposes the fatal flaws in North American hot water heating methodology like an off-grid install. You need to do everything right in order to get something you can live with. You want a Vedolux for burning wood or a 3-wood for burning coal - no electrical crap to waste power and break on you. I see you live in AB, good thermal coal from the Dodds mine is only $40/tonne. Coal frees you from boiler stokery even more than wood w/storage (no need for storage with coal for further savings) and no need to cut/split/dry - think about it.

A properly designed off-grid power system is way MORE reliable than grid-power, but you still need to ask yourself "what happens if the lights go out?" In the case of the Garn, the fan stops and the unit chokes. The loss of pumps is less of a problem if you allow for gravity circulation. If your boiler requires no power, you can gravitate through a blackout - you are warm and your pipes dont freeze until you can work things out. You will need way less panels & batteries. There is no point cutting the umbilical to the Oil Man only to establish a new one to the Electricity Man.

grainfedprairieboy said:

Last fall I purchased a Garn 1500 and this spring I plan to hook it up. I am trying to put the electrical requirements of the house heating system (including indirect DHW circulation); on a solar/battery system so I am sensitive to the electrical consumption of various pumps, particularly the one from the Garn to the heat exchanger as that will be continuous 24/7 & 365.

Within the house to the different zones I am planning on using the very efficient El Sid 20 pumps that are rated for 5 gals.

My problem is trying to move hot water from the Garn which is 95 feet and 10 pressure head from the heat exchanger in mechanical room in the basement. The volume I calculate for the required BTUs is 14-20 gal/min. Since finding a long life low wattage dc pump with that capacity seems almost impossible I am considering using 4 or 5 el Sid pumps.

What I do not understand is how exactly to hook them up so it would actually work as I'm no plumber by any stretch. Would it be best to have a manifold off the Garn and run 5 separate delivery and return lines underground? If I did this would I require 5 small heat exchangers or just a single manifold where the lines could come together at one large heat exchanger?

Or am I just way out to lunch? Any help or advice would be greatly appreciated.

Click to expand...

Hmmmm..looking at the pump chart for the El Sid 20 it would appear that it will do 5gpm but only up to 2' of head. .....if I'm looking at the correct chart that is. http://www.altestore.com/mmsolar/others/DC_Circulating_Pumps_Brochure.pdf

If that is indeed the pump you are looking at, the tubing size and the heat exchanger will have to be selected with ultra low head in mind. If I'm reading your stats correctly, (14-20gpm@10' head) you are far beyond the capabilities of an El Sid of any type. No matter how many you stack on top of each other. A number of 809's would develop 10' of head at a flow rate of less than 4gpm. You total wattage would be upward of 300

If you can manage to find a 12V circ that will do even 3 gpm into 10' of head you will need 5 or 6 of them to get up to your 14-20gpm range. You'll want to go with 1-1/2" tube from the Garn to the house or a combination of smaller sizes that would equal that capacity.

Piping would be as follows. Use 1-1/2" steel from the Garn to a series of 5 (?) tees, each with it's own circ on it. Then from the outlet side of the circs you would/could go back into another set of tees and into a single pipe/tube going to the house. The single line would go to your house then back to the Garn in at least the same diameter. Note that there is far less surface area on a single 1-1/2" tube compared to using 5- 1" tubes to achieve the same head loss.

Personally, i would advise backing up a bit and thinking very hard about designing some type of heating system for your house that can work with a very large temperature drop. The more temp differential you can generate, the less flow you need.

As heaterman says, look at your design and see what you can do to maximize your delta T.

Look at equation 1 in http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

Your required flow rate is inversely proportional to your delta T...

So if your calculated required flow for your load is 14-20gpm and that is assuming a delta T of 20F (please verify).

If you can support a delta T of 40F, then you can go to 7-10gpm and finally a delta T of 60F (not sure of the system) would be 3.5-5gpm which is in the range of your el-Sids.

el-SID have been around for a while and appear to be good, but check out some alternates like http://www.acs-solarsystems.com/Solar_Pumps.htm

Finally, I assume you have an inverter to run some appliances - so do the math on the benefit of dc versus ac pumps - especially the new ecm pumps mentioned previously.

There is a good article on heating 2500 sq ft on 40W at http://www.pmengineer.com/Articles/Cover_Story/BNP_GUID_9-5-2006_A_10000000000000187323

A Caleffi Solar will do 3gpm at 10' of head. But its drawing 40 watts to do that. And thats at 24 volts. But 24V is the way to go. 12V is fine for small cabins with the basics, but if you want boilers and appliances, go 24V. You really need to get the head down. Size your pipes on the large side, to reduce head and aid gravitation during blackouts. An outdoor boiler really is a luxury off-grid. You need to pump through every foot of that extra pipe. I have heard of a Hutterite colony that built the colony near a coulee and put a Homesteader OWB down on the grade and gravity-fed from there. That would be the only economical way to work an outdoor unit, not to mention the bulletproof reliability (gravity is always "on").

I have a major beef with that Sigenthaler article. It's content is still considered "radical". That's a shame, because JS is headed in the right direction here. To his credit, I think the intention was to get people thinking and talking, but this concept is still clearly in the incubator. He says 40 watts, but that only counts the load circ. I count 3 circs in the diagram. The house needs over 60k BTU and the boiler is sized to "rapidly charge the buffer tank" so you're looking at say a 80 to 100K boiler. Thats 8-10 gpm and very little head but another circ none the less. Then you add the boiler fan. Then you add the fancy controls. Then you add the DHW circ - how much juice is that, Jonny? He conveniently left all that out. Simply by putting a tall hydro-sep by the boiler and (there's that word again) - *gravitate* into that, you eliminate a circ, which only wastes power and breaks on you. With the insane price of batteries these days, I'd be shaving every watt.