HX for DHW

[NHFarmer]

I am going with a non pressurized storage tank.I am planning to use a coil for domestic preheat then on to a Superstore.I am then planning to use a circulator pump on a separate zone to bring the tank to its final temp.Has anyone just used the storage tank with a coil and no superstore?Any ideas if this would work?I imagine I would need a larger coil,but it would save the cost of the superstore

 

[MrEd]

If I am not mistaken, when you buy a complete system from Tarm, with the STSS tanks and copper coils, one of the option is to have a domestic coil in the tank - so I'd say yes, it has been done and probably by lots of people.

 

[Nofossil]

I have almost exactly the system that you're proposing. In my experience, the SuperStor is invaluable because it gives you the option of heating only the 40 gallon SuperStor with a backup source when your wood or solar is not keeping the storage hot enough.

You need a LOT of copper to get 115 degree water out of a 120 degree storage tank, by the way.

 

[MrEd]

So, if you were going to have a big (unpressurized) tank, say 1000 gallons or more, would it affect your decision about what size superstor to get? In other words, does it make less sense to purchase a 80 or 100 gallon superstor if it is being pre-warmed in a DHW coil in a tank?

Also, any thoughts on using a conventional electric hot water tank instead of a superstor? I am thinking about putting a coil in a unpressurized tank and then passing that into the cold-water-in of an electric tank....so the electric is available as the backup. I'd rather have a superstor (I think), but the electric tank is free, and the superstor is close to $1000

 

[Nofossil]

So, if you were going to have a big (unpressurized) tank, say 1000 gallons or more, would it affect your decision about what size superstor to get? In other words, does it make less sense to purchase a 80 or 100 gallon superstor if it is being pre-warmed in a DHW coil in a tank?

Also, any thoughts on using a conventional electric hot water tank instead of a superstor? I am thinking about putting a coil in a unpressurized tank and then passing that into the cold-water-in of an electric tank....so the electric is available as the backup. I'd rather have a superstor (I think), but the electric tank is free, and the superstor is close to $1000

I have a 40 gallon superstor and it's fine for a family of five. You'll have to put a mixing valve on the output since you have the possibility of getting scalding water out of it. The mixing valve also lets you overheat it (I run mine to 160 degrees) which gets you a lot of use between firings.

You can use an electric, but the advantage of the superstor is that you can heat it directly from your boiler and/or storage. Some folks use an electric with a sidearm. Not a bad way to go. There are plenty of threads on sidearm heaters if that's not something you're familiar with.

 

[MrEd]

I'll read the sidearm threads - never tuned into them 'cause they didn't apply to my situation at the time.

Do you have any stats (or gut feeling) how much if anything pre-heating your DHW in your big tank helps the little tank? Any way to quantify it? Obviously any help is good, but there is that whole "point of diminishing returns" thing to think about...especially with the cost of copper.

 

[NHFarmer]

It sounds like the Super stor or a side arm is the way to go.Nofossil,I like having the option to use multiple heat sources.I am planning for a tempering valve to allow for higher tank temps.I am all ready spending plenty so the additional copper doesn't seem worth it.

 

[Nofossil]

It sounds like the Super stor or a side arm is the way to go.Nofossil,I like having the option to use multiple heat sources.I am planning for a tempering valve to allow for higher tank temps.I am all ready spending plenty so the additional copper doesn't seem worth it.

I'd do mine differently today based on the cost of copper. If you go with a tempering valve, I'd recommend the Honeywell AM101 series because they allow the output to be as close as three degrees to the hot inlet. Most don't mix with that small a difference.

 

[NHFarmer]

That is exactly what I ordered for a tempering valve.I am planning to set it up the same way you show it on your website,Thanks

 

[mpilihp]

NoFossil I was looking at your diagram (Nice Job) and have a couple of questions

WHats your tankless propane heater rated for and roughly how much does one cost??

I see you have a flat plat HX for DHW, as a backup im assuming, if your storage tank supported heat up to 170 deg couldnt this be used as a primary means of heating DHW wheather the water used to heat it came from your backup propane heater, wood boiler or storage tank?? Looks simple to me, I like it.

How does the system decide to activate the DHW circ so it draws DHW from the HX instead of the superStor?

THanks

~ Phil

 

[Nofossil]

NoFossil I was looking at your diagram (Nice Job) and have a couple of questions

WHats your tankless propane heater rated for and roughly how much does one cost??

I see you have a flat plat HX for DHW, as a backup im assuming, if your storage tank supported heat up to 170 deg couldnt this be used as a primary means of heating DHW wheather the water used to heat it came from your backup propane heater, wood boiler or storage tank?? Looks simple to me, I like it.

How does the system decide to activate the DHW circ so it draws DHW from the HX instead of the superStor?

THanks

~ Phil

My tankless is a Takagi T-Kjr, which is rated at a max of 140,000btu/hr. I paid under $500 with shipping. The flat plate HX is not actually necessary. I put it there to get instant response if the DHW temp drops too low. The aquastat on the DHW tank assumes a good bit of stratification, so it's actually set at a fairly low temp - about 105 degrees. With all the odd thinkgs I'm doing, there can be times when the DHW is not so stratified, and I want to get heat very quickly if the DHW needs it.

The system doesn't decide anything as far as where it draws water from. If the DHW aquastat is calling for heat, then the DHW circ is running. Water is being drawn from the bottom of the DHW tank, heated via the flat plate HX, and returned to the top of the tank. DHW is always drawn from the top of the tank. If you're drawing DHW as it's being heated, some of the water you're getting will have just passed through the HX.

 

[mpilihp]

Thanks for the info on the propane heater, as for your DHW setup im alittle confused. The DHW aqustat when it calls for heat its opening zonevalve Z1 so whatever heat source is avail will heat the superstor tank correct? Your saying this also starts the DHW cir pump? The DHW circ pump is pumping the actual DHW through a HX, os it could be pumping water from the bottom of tank through HX and back into top even though there is no system hot water in the HX to transfer heat to the DHW?? From the diagram it looks like the DHW HX will only get hot water from the propane heater, Im just trying to understand, I like the idea and the setup, if I can get rid of my Oil beast and its need to have its belly heated I will.

 

[Nofossil]

This really should be another thread. I've attached the diagram for those who might be wondering what on earth we're talking about.

In the current scheme, the Z5 segment has been left out. When the DHW aquastat calls for heat and the wood boiler and storage are both too cold, Z1 is opened and both the Propane Heat circ and the DHW circ come on. Flow through the tankless heater causes it to come on. Boiler water circulates through the tankless heater to the flat plate HX, then through Z1 and the DHW coil. At the same time, the DHW circ is pulling cold potable water from the bottom of the DHW tank, running it through the flat plate HX, and returning it to the top of the DHW tank.

Apropos to the original topic, this diagram show how I've configured my preheat coil from storage and my two mixing valves.

 

[mpilihp]

Again thanks for the explaination, do you mine telling me where you purchased the T-Kjr for that price? Ive seen it on the web for over $600, still a deal compared to trying to buy it from a supply house without a boiler cert.