water to air Hx for heat dump loop?

[mole]

Hi all,
I'm looking for a little help today on a dump zone design.

I've been using a power inverter/battery backup for my Seton 100 in case of power failure. After a year and half, the first one died. Now the second one is acting up after a year+ (just beyond the warantee). They were relatively cheap ($250-300) inverters. I can't see buying a third one, so now I'm planning on installing a dump loop instead. I s'pose I should have done that the first time around. Hindsight is great.

I have a couple of questions:

1) I have limited space above the boiler for fin/tube baseboard type hx. I was wondering if anyone has successfully installed a water/air heat exchanger as an alternative to the fin/tube approach. I see 18"x 20" or 17"x22" for $220 or so. This would fit in the available space better. My concerns are that the narrow (3/8") channels may limit gravity flow and also I wouldn't know how to size one in a "radiant, gravity flow" mode. On the other hand, it would make for a very short loop, which might be a plus. Any thoughts?

2) I'm planning on 1" copper pipe from the boiler to the dump zone and a NO zone valve. But when I look at valves for sale for this application (houseneeds.com), I see they only carry 3/4" and they are specifically for this application. So is 1" overengineering it?

3) If I install the zone valve on the hot water outlet of the boiler will I get ghost flow from the boiler return line back up to the Hx? Should I be installing two NO zone valves, one on each end of the loop, or is that overengineering it? Would like to hear anyone's experience (hindsight)!

Thanks for the help.
JR

 

[stee6043]

Are you talking about the HX's designed to be used in a furnace plenum? Without a source of air movement (fan) I'm betting you won't be able to bleed off enough heat with such a small HX. And having a fan would defeat the purpose of a powerless heat dump.


What kind of inverters are you buying? I have a APC UPS that can be found used for your price range and the thing will run forever. Worst case is I have to replace the batteries once in a while ($70 for the pair). You may want to research better battery backups if you don't have space for fin/tube. Or mount your storage above your boiler! ha.

 

[mole]

Stee,
Yes, I'm talking about the plenum mount type. You may be right about not getting enough air flow. I have no logical basis to expect it to work. My thought was that if I got one that puts out 120,000BTU @180F with fan, maybe without it I could eek out 10,000-15,000 BTU by convection and 190-200 degree water? That may be all I need.

My first inverter/charger was a 100W Power Express, The second one is an AIMS 1500. All I power is one Taco 007 pump (.8A@110V). I need it to run for 12hrs though due to the large themral mass of the Seton. Does this APC UPS take special batteries?

Thanks
JR

 

[pybyr]

As per Hot Rod Bob Rohr's suggestion to me, skip the inverters- get a Laing 12vdc solar circulator pump, a gravity weight check valve, a trickle charger, a trolling motor 12 V battery, and a 120 VAC relay. Put something like a big loop pf copper or scrap-salvaged fin-tube up for your dump zone- or, in my case, a dented but non-leaking Euro-flat-panel-radiator.

Normal situation: power on, system normal, battery trickle charging.

AC fails, relay kicks on the 12 VDC solar circulator powered by the battery; heat dissipates, boiler is happy, life is good

 

[mole]

Pybyr,
That's an excellent idea! I suppose if l plumb the 12V pump parallel with my Taco 007 and add a couple of check valves, I can continue to use my storage tank as the heat dump.
Thanks!
JR

 

[Gooserider]

Most UPS units run on "Gel Cell" batteries, which are essentially a spill proof version of a lead acid battery. The number and voltage of the batteries tends to vary with cheaper units running on one 6 or 12 volt battery, and more expensive units using several in series... I have some ON-900's that run on 4 x 12v batteries, and some APC 800RT's that take 4 x 6v batteries (I'm trying to sell some of my extra APC's)

I haven't done it, but I've heard that one can replace the gel cells with deep cycle marine batteries wired to match the voltage, as long as you are careful to properly box and vent the marine batteries, and keep them away from the UPS electronics... This would give considerably longer run times, but I'm not sure it would be enough given what you say you need for your system.

Gooserider

 

[rkusek]

Gooserider, I was contemplating trying a couple deep cycles with an APC to extend the run time significantly. Does anyone have any experience doing his? Also, what do you guys think of Mole's version of Pybyr/HR heat dump solution? For those of us that can't find fin tube this sounds like the perfect solution

 

[Gooserider]

Gooserider, I was contemplating trying a couple deep cycles with an APC to extend the run time significantly. Does anyone have any experience doing his? Also, what do you guys think of Mole's version of Pybyr/HR heat dump solution? For those of us that can't find fin tube this sounds like the perfect solution

As I said, I haven't done the battery replacement thing.

I don't know how the numbers work out on the Pybyr / HR approach, i.e. if the pump would move enough volume to do the job, and / or the battery keep it running long enough, but if they do it should be fine... Also you might need to replace the battery every few years, and it might be hard to tell (absent occasional testing) when that is needed.

Gooserider

 

[mole]

I figure the Laing D5/720 would move between 3-5 gpm in my loop, which should be sufficient if the fire is going out. It looks like it should run for a couple of days from a single 105 amp-hr deep cycle battery, since it only draws 1.4A. http://www.lainginc.com/pdf/LTID5solar.pdf. (broken link removed) Pump cost is a little steep at about $210-250. It looks like an internal check valve is included in the models from HouseNeeds.com.

JR

 

[pukendawg]

If you have a UPS that has battery issues, borrow a good battery tester from your local garage and hit the Auto Zones/ Advanced Auto, Sears ect. and ask if you can buy a couple cores off of them. If they are OK with that start testing batteries. These are do it yourself places and throw out about as many good batteries as bad. They work great in a UPS. Take the UPS apart and you may have to lengthen the leads and bang, you got a good UPS. The batteries with the corners missing from the cell covers are Johnson Controlls/Interstate batteries. They love you long time. Today's testers fit in one hand and weigh 2 pounds and are dummy proof and the battery can be tested in a discharged state. Hope this helps..

 

[in hot water]

remember the dump zone needs to keep the boiler temperatures in a "safe" zone in the event of a power outage or very small load condition. So you don't need to size for continuous boiler output, just enough to keep the boiler or storage below 200F for example.

Most boilers rev down fairly quickly when the power goes out. Unless you open the door or allow O2 into the fire.

If you find your system in "dump" condition for a extended periods you may have too much "horse power" or maybe more storage would be a good addition.

hr