Oil Indirect DHW - Cost Analysis Help

[Ashful]

I'm a bit late to this thread but I installed a Geyser HPWH 3 years ago now.
Pictures are in: https://www.hearth.com/talk/threads/ducting-and-geyser.108580/

Saved 1 gall of oil per day.
The most pleasant surprise was the drop in AC costs in summer.
The oil DHWH is inside the air conditioned volume of our house and so the AC had to shift the waste heat from the oil burner as well as the general house heat.
In our case, when all done, we got summer DHW for just about free and in the shoulder seasons, a barely changed overall electric bill.

Okay, I'm confused by this:

This shows how the Geyser was plumbed in parallel with the 80 gall oil water heater.

So, you installed in parallel, and I'll assume the reason is so that you can throw a pair of valves and run off either oil (winter) or HPWH (summer). However, why wouldn't you just plumb them in series, with the HPWH up-stream of the storage for the indirect oil? As already mentioned here, the oil indirect would be reduced to just maintaining the water coming off the HPWH in summer, and could be set a little lower than the HPWH, so it cycles only under extremely long storage situations. It would give you significantly more storage, and rather than switching valves twice a year, you could just kill the breaker to the HPWH in winter.

What did I miss?

 

[Redbarn]

My layout is very simple.
For all but 30 days per year, the oil burner is turned off.
The Geyser draws water out of the bottom of the 80 gall tank and returns hotter water back to the top. No oil is used.
When we get house guests, the oil burner is turned on and both often run together which dramatically increases hot water response time. Both heat the same 80 gall tank of hot water, often simultaneously. The oil heater is governed by its own aquastatt.
In winter, the oil heater is turned on but power to the oil burner is governed by an air thermostat that turns it on if the basement temperature drops below 52 deg F, the temp at which the Geyser starts to struggle. The oil burner quickly heats the 80 galls and the Geyser shuts off. As warmer weather arrives, the temp in the basement rises and eventually the oil burner is shut off again.

 

[Ashful]

Very cool. I think I'm sold on the HPWH concept, particularly for seasons when the oil burner is not being used for heat. Whether it makes sense to run a HPWH only 3 months, 6 months, or 9 months of the year, when you already have oil indirect running, is probably matter for a whole other thread. But, I think I'm going to start looking into adding a HPWH to my setup, nonetheless. In my case, I had imagined a HPWH with a tank, plumbed in series with (upstream of) the boiler's indirect DHW. So, the HPWH heats incoming water, and the old DHW tank is set lower to act as additional storage. Since our current DHW seems to have more capacity than we need, tho... maybe it makes more sense to do a tankless HPWH on the same oil indirect DHW tank, and just set the oil T-stat to a much lower temperature than the HPWH T-stat.

 

[Redbarn]

I could see no sense for me in installing a separate tank HPWH. Our 80 gall DHW tank was in good shape and all I could see was heat losses and lots of plumbing & control system issues.
If I were replacing an existing DHW tank, then a HPWH with tank would make sense.

I just engineered things so that the HPWH carried as much of the DHW load as possible with the oil DWH heater covering shortfalls.

 

[Ashful]

Was looking at the Geyser RO literature, and how I'd hook it up with the boiler mate. Interesting, but it seems to me they focus on making all the installs too DIY friendly for my tastes. Might check out their commercial stuff, but also want to check other mfgr's.

 

[Redbarn]

The Geyser installation is really pretty easy. Very straightforward.
I watched Tom in Maine's video before I did mine.

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You could always hire a professional to do it. They'll make it a more complex job.

 

[Ashful]

Hah! No, you misread me. I grew up working as a plumber's apprentice (father's family owned a plumbing business), and tend to shy away from DIY type appliances when it comes to plumbing, as they never seem to have a great track record in the long-haul. I think we're probably only two or three decades out from learning PEX is the next polybutylene, or finally discovering the health effects of having your drinking water indefinitely soaking in polyethelene tubing.

I just finished re-plumbing this house, all in copper (1" mains, 3/4" runs, 1/2" appliances), and hate the idea of that Geyers RO box sitting on the floor with its plastic lines running to my beautiful BoilerMate. I'm also a little confused by the need for the dip tube in most installations, thinking the "Alternate Installation" on p.16 seems to be the only sensible one (of course... if you could replace the plastic tubing with copper):

(broken link removed to http://www.nyle.com/downloads/GeyserRO_Manual.pdf)

I like the idea, but dislike the Geyser residential units. Maybe their professional units are more suited? Our hot water usage is probably higher than the average residence, but their pro series looks maybe TOO big (24k BTU vs. 6k BTU). Seems to me I should be shopping 10k BTU units, but that's just a rough guess.

edit: I see no mention of it in their manual, but I am finding some Geyser RO install photos that are hard-plumbed with copper. That's promising.

 

[Redbarn]

My father also owned a plumbing business so I have little fear of plumbing. However, I never developed a love of installing copper piping, just too much work to achieve the simple task of routing water from A to B. There is a certain beauty however in a nice pipe layout. I just love Pex.
The Geyser is not a consumer grade product. It is a piece of industrial equipment that has strayed into the consumer market. It is pretty rugged. Mine survived being 50% immersed in basement water (while running !) during Hurricane Irene.
The page 16 layout is the only sensible installation scheme.

If you need 10k BTU or more then the Geyser is too small.

 

[SIERRADMAX]

My father also owned a plumbing business so I have little fear of plumbing. However, I never developed a love of installing copper piping, just too much work to achieve the simple task of routing water from A to B. There is a certain beauty however in a nice pipe layout. I just love Pex.
The Geyser is not a consumer grade product. It is a piece of industrial equipment that has strayed into the consumer market. It is pretty rugged. Mine survived being 50% immersed in basement water (while running !) during Hurricane Irene.
The page 16 layout is the only sensible installation scheme.

If you need 10k BTU or more then the Geyser is too small.

I agree pex is easy. But for those with rodent problems, mice don't like the taste of copper!

 

[Ashful]

My father also owned a plumbing business so I have little fear of plumbing. However, I never developed a love of installing copper piping, just too much work to achieve the simple task of routing water from A to B. There is a certain beauty however in a nice pipe layout. I just love Pex.
The Geyser is not a consumer grade product. It is a piece of industrial equipment that has strayed into the consumer market. It is pretty rugged. Mine survived being 50% immersed in basement water (while running !) during Hurricane Irene.
The page 16 layout is the only sensible installation scheme.

If you need 10k BTU or more then the Geyser is too small.

Cool, thanks Redbarn!

On the actual need, I'm quite unsure. We're currently a family of 2 adults + 2 small children, so our needs are sure to grow as the children do. We have frequent house guests, and I suspect it won't be uncommon to have three showers going simultaneously to one or two dishwashers and even a washing machine. I really need to look at my current usage, to determine what size heat pump makes the most sense. With the boiler, I have options to have the boiler kick in any time the heat pump lags behind, and in fact might not even use the heat pump during the months of the year when our hot water load is probably highest.

I love the home-run architecture that PEX permits (imagine the cost in copper!), versus the more confusing distributed architecture one uses with copper. However, copper has a track record that is impossible to deny. Every other plastic system we've introduced has come up short in one regard or another... eventually.

A side story to that side story.... When I re-plumbed my house, I drew the layout and went to buy all the material. Copper had gone up in the few years since I had last done a similar project, so I experienced a little sticker shock when I left the supply house with $1800 worth of tubing and fittings. My house had been modified and expanded by several prior owners, to the point where there were 5 layers of piping hanging on one another, randomly criss-crossing the boiler room. Every time an appliance would shut off, all the piping would jump and clang against each other. There were runs of piping that went from the source, to the far end of the basement, just to come back to an appliance on the same side of the basement as the source. A true mess, with miles of wasted pipe and dozens of old valves frozen shut or open. I cut it all out, saving any good tubing, and found I had so much recovered old tubing that I only ended up using two 10-foot lengths of the new tubing I had bought. I ended up returning almost all of the tubing I had bought, and the few spare fittings I had bought, and found my total outlay was maybe only $700. Then I took the old fittings and remaining scraps of old tubing to the scrap yard, and got $500 for that. Total re-plumbing of the house only cost me roughly $200.

 

[Ashful]

The page 16 layout is the only sensible installation scheme.

Oh, meant to comment on this. I watched your video last night, and I had never seen that show, but I like it! However, I thought he mentioned several times running his system in reverse to what the manual (and my common sense) dictate. It sounded like he was going to pull cold water off the bottom of his tank, and return the hot water to the top. He said it more than once.

 

[Redbarn]

I don't wish to ignite a water storage temperature stratification debate, but I draw off the bottom and return to the top of the tank. The aquastatt for the oil burner is near the bottom too, so if the bottom gets too cold, it kicks in to support the Geyser.

 

[Ashful]

I don't wish to ignite a water storage temperature stratification debate, but I draw off the bottom and return to the top of the tank. The aquastatt for the oil burner is near the bottom too, so if the bottom gets too cold, it kicks in to support the Geyser.

Hmm... there shouldn't be a debate on this. There should be data to show which method is more efficient. Perhaps the only room for debate would be that usage patterns vary, and perhaps one method favors certain usage patterns better than the other.

Where's woodgeek? Stuff like this is his usual bathroom reading material.

 

[Ashful]

Hah... I just caught myself reading a site called treehugger.com! What are you guys doing to me? I feel so un-clean...

Next, I'll be putting insulation wrap on all my hot water pipes...

 

[Redbarn]

Insulation wrap on hot water pipes does work. I did some tests with an IR gun and could see a worthwhile difference.

 

[chken]

Hah... I just caught myself reading a site called treehugger.com! What are you guys doing to me? I feel so un-clean...

Next, I'll be putting insulation wrap on all my hot water pipes...

What, I read treehugger and I've got insulation on my hot water lines, what am I doing wrong?

 

[velvetfoot]

I have the gray insulation stuff on my COLD water pipes and I still got condensation. Perhaps if I do get a HP DHWH that would change.

 

[simple.serf]

I actually just stumbled across this thread, and the issue of DHW has been one I have been debating for some time. We have an indirect HW heater running off of an oil fired boiler. I am familiar with using heat reclaim systems from work (we use heat reclaim tanks to take waste heat from large refrigeration racks). DHW for us at the house has been about $1400/year.

One of these geyser units look like it may help us get to the goal of being off of oil altogether. The other advantage that I can see is that my genset can run this system, whereas an electric tank or an electric demand heater would be a little too much for my old MEP-002a. Plumbing it in copper would be a piece of cake.

 

[Redbarn]

I have used my Yamaha 2000 genny to run the Geyser but it took nearly 5 hours to heat an 80 gall tank full.
It was better to use the genny to run the oil water heater instead. We got a tank full in under an hour.

 

[Ashful]

I have the gray insulation stuff on my COLD water pipes and I still got condensation. Perhaps if I do get a HP DHWH that would change.

Probably not, unless your basement is exceedingly small and air tight. The condensation is from humid air hitting the cold pipes, and since that insulation isn't air tight...

The HPWH will remove some humidity from the air, but everything I read says that's pretty minimal. After all, how many minutes/hours per day do you expect this little Geyser to actually run?

 

[velvetfoot]

I didn't realize it was only minor-I hadn't read that.
Of course the basement was humid, from a relative point of view. That gray stuff is porus; it was like a sponge. I'm thinking the more rubbery stuff used on A/C pipes might be better.Wouldn't the hpwh be making the basement even cooler in the summertime? I should wheel it outside under the deck in the summertime. You know, I'm only half kidding.

 

[Ashful]

In theory, it makes the basement both cooler and dryer. However, maybe not enough so to keep up with fresh air infiltration, especially in a larger basement or one that's not well-sealed from unconditioned space above.

I think you'll have the same condensation results with any form of insulation on the cold water pipes. The only solutions I know for this problem are warmer water or dryer air. Do what you can to seal the basement, and then install a dehumidifier. If you're set on a HPWH, it might be worth waiting to see how well it dehumidifies, but unless you use a lot of hot water to where you're keeping it running for a significant portion of the day, what I've read indicates it's only offering fairly minor help in cooling and dehumidification.

 

[velvetfoot]

Joful, I've got to get some sleep now, but if you can recall any links dealing with the dehumidification effect of hphwh's I'd appreciate it.

 

[Redbarn]

A Geyser is a serious dehumidifier. It has an 8" dia inlet/outlet and moves a lot of air.
The basement containing the Geyser is circa 2000 sq ft and if it runs for 5 hours a day, it dries it out pretty thoroughly.
We own other dehumidifiers and these are toys by comparison.

It all depends on the size of your basement, your air exchange and wall seepage.
Any HPWH would do a good job at dehumidifiying.

 

[Fred61]

I installed my Geyser last spring hooked to a 40 gallon Superstore. Basement is 1000 sq. ft with several uninsulated cold water pipes that seriously condensed in the past.
The Geyser not only cooled the space but dehumidified it to the point where I invested in a duct booster fan to direct some of the air up to the living space. This greatly reduced the operating time of my mini splits over the whole summer.

I didn't measure the humidity level nor did I calculate the amount of hot water used and only took a quick glance at my electric bill to see if anything outrageous stuck out but we are hot water hogs here perhaps spoiled by the cheap wood fired water we enjoy all winter.