Looking to install geothermal pluming question

[lostDuck]

Ok so a little off topic for this site but you all have been a source of great info I thought I would ask my question here.

So I am looking at installing a Ge Hybrid hotwater heater but i ran into some issues i think. The plumbing looks like both the oil boiler and electric hot water heater are feeding the hot water line in parallel. Shouldn't the flow be oil to electric to hot water feed in serial so that when the oil boiler is on the electric hot water heater is just acting as a storage tank?

See picture.


I appreciate your help.

 

[semipro]

Your proposed change makes sense to me as long as:

1. Running cold water through your boiler when its not heat doesn't somehow damage it. (condensation, scaling, erosion corrosion, etc.)
   
2. The additional resistance of adding series piping doesn't lower your water pressure/flow at the tap unacceptably.

Another scenario might involve placing the mixing valve after the electric water heater The benefits are added overall hot water capacity of the system because water can be stored at higher temps without the risk of scalding to users. The higher temps prevent the growth of bacteria in the system. The downside is that the higher temps in tanks and piping will result in higher heat losses to the room. Heat loss is faster when temp differences are greater.

 

[maple1]

I think I would bypass the oil unit all together.

 

[velvetfoot]

If the electric is turned off in the wintertime, how does the hot water in the oil indirect tank get over to the electric water heater when no fixture is turned on? Wouldn't the water cool off on the way through it? I myself wouldn't mind using the indirect tank as a tempering tank in summer because I have cold well water, but haven't gotten my head around the issue I mentioned first. I just valve off one or the other depending on the season.

Edit: You didn't mean to have geothermal in the title, did you?

 

[lostDuck]

velvetfoot, agreed i did not mean geothermal... how do i change title.

All, the issue at hand is that
in the summer the hot water gets cooled down by the cold oil furnace water.
in the winter the hot water gets cooled down by the cold electric hot water heater which is off.

velvetfoot you mentioned something that i dont have... neither of the units have on off valves. is it just as simple to add valves to each of the hot water outlets?

 

[velvetfoot]

velvetfoot you mentioned something that i dont have... neither of the units have on off valves. is it just as simple to add valves to each of the hot water outlets?

At the alway present risk of being wrong, I would say "yes". Are you sure you don't already have valves? I would think you'd want to have them in case you want to change out a unit.

I think you can edit a title by going into editing post. Too much time can't have elapsed though.

 

[lostDuck]

I updated the diagram.... No there are no hot water shutoff valves it looks like a handy man special... just like everything else in the house... :<

 

[woodgeek]

Keep in mind oil-heated HW is often more expensive per gallon than HPWH-heated HW, even in winter. Tell me your kWh (prob high in CT) and oil cost and I'll break it down.

 

[lostDuck]

thanks electric is 18.5 cents and oil is 4.09

 

[maple1]

Keep in mind oil-heated HW is often more expensive per gallon than HPWH-heated HW, even in winter. Tell me your kWh (prob high in CT) and oil cost and I'll break it down.

The primary reason for my post. I would forget about heating DHW with oil all together.

 

[woodgeek]

thanks electric is 18.5 cents and oil is 4.09

Simple answer:
a million BTUs of DHW:
(at Delta_T = 50°F (at shower) this makes ~3000 gals of HW)

HPWH: 1e6 / 3414 kWh = 292 kWh / (EF = 2.3) = 127 kWh * $0.185 = $23

Oil: 1e6/1.40e5 BTU/gal = 7 gallons /0.75 EF = 9.5 gallons * $4.09 = $39

In the summer, your EF on the oil boiler is prob closer to 0.25 than 0.75, and you are over $100/ millions BTU.
In the winter, heat stealing causes the HPWH cost to be somewhat higher, depends on how conditioned the space is, i.e. whether you are running more space heating, or recovering heat that would otherwise be lost (e.g. a slightly cooler basement just loses less BTUs to the earth).

Personally, I'd run it 12 mos, and shut down the boiler all summer.

 

[maple1]

I don't think we know for sure - is this oil unit an indirect tank, or is it a tankless coil? I don't know what the data says, but I think a tankless coil is a lot less than 0.75 at the very best of times.

 

[woodgeek]

To clarify...I assume 25% of the oil BTUs go up the stack. 75% does NOT end up in the water, but in the winter, the parasitic loss BTUs can contribute to space heating. Ignoring that effect, the EF is prob <25%, and the cost of 1 MMBTU in hot water is >$100. Never had an indirect myself, but I am skeptical that they are any better on (non cold-start) oil boilers.

oil hot water in 2014 == bleeding money.

 

[lostDuck]

All,
I appreciate your input. I have re-plumbed the setup and installed the ge hybrid hot water heater. Now that both systems have shutoff valves i can determine which system (or both) that I want to use.

I appreciate all of the input and woodgeek thanks for doing the math for me.