certified freak seeks help with system design

harold campbell

If you like problem solving/ designing, do I got one….. it’s long, so I don’t blame you if you get bored and don’t reply.

So here’s the plan/problem, any suggestions or recos greatly appreciated. I have old house (1600 sg. Ft.) in Northeast with 20+ year old oil fired 150000btu boiler, 5 year old storage tank from tankless coil in boiler for DHW, 3 zones w/ taco 007 circs/24v relays off programmable thermos for heat . I have no (little) money and I am getting killed by oil bills and desperately need relief. To further problem, I probably won’t be in house past 7-10 years so can’t do anything with long payback time. I know beggars can’t be choosers but I would like to do something to offset my bills with some efficiency.

I initially looked in tk-jr tankless heater (have gas to house already) to offset hotwater costs, with $300 tax rebate it is doable, and saw it can be used as heat source to supply radiators if properly plumbed. Did research on primary secondary etc.; and found test done in Minnesota to supplement old boilers with new high effeciacy boiler and came up with plan (scheme) to do same in my house. I would like to reuse as much as possible from my old system (expansion tank, supply valve, circs, etc.) and misc. heating parts inventory.

I have available assuming I get tk-jr by 12/31/06:
Takagi tk-jr
Old oil boiler
3 taco 007 circs with associated Honeywell 24v relays
honeywell Aq475 outdoor reset (recently bought, but not installed yet)
2 taco gold zone valves (not currently used in system)
Storage tank w/ taco 006 bronze circ and aquasat

I originally tried to design “best case” primary secondary system, allowing flexibility to add new components as budget allows, and soon realized I would need 4 more 007 circs, (or one expensive high head 011 circ and 2 007’s), plate exchanger, numerous check valves, etc. The system I thought up would consist of smallish secondary loop (main loop?) with taco 007 circulating water around it. The tk-jr would be plumbed into (actually away from it) this loop via closely spaced tee’s with taco 0011 or (2 taco 007’s in series to overcome high head need of tk-jr). the 3 zones, each with own 007, I currently have would be plumbed away from secondary (main) loop via two closely spaced tees (two separate branches, one for supply, for return). The plate exchanger would be plumbed off main loop with closely spaced tees with own 007 circulator controlled by storage tank circ/aquasat. The old boiler will be plumbed off secondary loop with two closely spaced tees and own 007, not to be used, but for emergency and to allow future upgrade to high efficiency boiler when I can afford it. It will be “disconnected” from system by closely spaced tees and no hot water will enter to be lost. The outdoor reset will control the secondary (main) loop temperature (sensor installed there), when call for DHW, controller shuts off heat zones, and raises secondary loop to 180 degrees, the plate exchanger draws off this and heats water sent to exchanger by storage tank. No condensing issue b/c tk-jr supplies the heat. In emergency, if tk-jr fails I can adjust outdoor to protect boiler and fire up oil boiler. When each zone calls for heat, it draws off main loop with own circ. Over $2000 though.

Boy would a sketch help here.

Now reality set in and I want to see if anyone can come up with hybrid that will work with what I already have with addition of as few new parts as possible. Here is what I have come up so far:

Plumb tk-jr to side wing of a “U” of piping via closely spaced tee’s, draw water to tk-jr by 2 007’s in series, put plate exchanger in pipe returning water from tk-jr to “U”. plumb old boiler to bottom of “U” loop via closely spaced tees with gate valve b/t them. No circ to push water off “U” loop to old boiler. In emergency, close gate valve and forced water to old boiler and fire it up. when tk-jr operating , gate valve open so no water enters cold oil boiler. buy one more zone valve and run 3 zones off these with remaining 007 circ I have. When there is call for DHW, reset cuts power to the one circ supplying to heat zones and zone valves and entire tk-jr. output runs thought plate exchanger and back in loop attached to “u”, giving priority. the heat zones draw and return water from and to the tops of the “U”. With this system I only need to buy the heater and one zone valve and associated piping. I would be getting heat from a much more efficient heat source than what I have. Also this would cost under $1000- after $300 rebate. When storage tank goes, I’ll replace with indirect.

Boy would a sketch help here………

Thanks to anyone who provides feedback, or ideas. Yes, I am a dull guy in need of a hobby (and life). If original system is so much better than “hybrid” I’ll bite the bullet, but don’t see what I lose with plan 2.

Part II (believe or not, I have more questions) will address sizing the pipes of the system, place of expansion and supply feed, etc. I wasted enough time trying to get you all to somehow envision this thing and cant do more if I don’t get any replies…


Thanks again.