Indirect tank designed for Condensing Boilers

johntrhodes81

I haven't seen one, but does anyone make a Residential Indirect Hot Water Tank that is specifically designed for Condensing Boilers? One that gets the return water temp low enough, so the boiler will be well into the condensing range, like through the use of an economizer so the incoming cold water can drop the temp of the return water?

Thanks,
John

bmwpowere36m3

I don't know.... but I'd imagine the recovery rate would be terribly slow. I've heard it said here that with with indirects you won't condense, so you might as well heat/satisfy them as quickly as possible. Don't want to be the second or third person taking a shower....

SWEI

The incoming cold water almost guarantees condensing during DHW production -- as long as the boiler water is moving slowly. Translation: Look for the largest HX area you can find.

Keeping the boiler condensing takes some tinkering with the controls, but it can be done.

njtommy

I guess if you use a lot of hot water it could be worth doing. Plate heat exchangers are not a lot of money. But I can't see your return water dropping below 120 out of the tank. So your at around 90% eff. With a 140 supply or so. It's some you would have to tinker with like swei said. Also your firing rate will increase as well dropping your efficiency. It will be a balancing act and a nice little project

njtommy

@Hatterasguy stop rubbing it in my face I know I should of gotten the HTP over the Navien. Lol

johntrhodes81

How about use 2 indirect tanks half normal size in series. Boiler water in to # 1 then #2. Cold water in to #2 then #1. Aquasat in #1 only. This way the boiler water return from #2 would be cooled the most by incoming cold water.

John

Hilly

What about those 'reverse indirect' tanks that run the water through the storage and domestic through the coil. Supposed to be boiler temperature requirements by design but I don't know if they are still low enough to condense.

njtommy

What temp does the current system use or what temp are you designing the system for heating?

johntrhodes81

I currently have a 180 degree system (oil fired ci boiler) but have enough emitter capacity to run 140 degree water on a design day switching to a HTP UFT-80W.

John

ced48

How can you heat water to 130 degrees or higher, and keep a condensing boiler always condensing?

Gordy

You guys are nuts. Eat the efficiency hit while making DHW. Your still making it at mid 80's efficiency for how long?....... Sheesh,

Gordy

You know what I mean......sometimes people jump over a dollar to pick up a dime. Just to say they did it. Two in directs what's the ROI for that in residential land?

Gordy

I only have one contact in tonight, in my dominate eye of course..........

njtommy

55 mins yup that sounds like my wife.

Mark Eatherton

Look at Turbomax. Only requires approach water temperatures 10 degrees F over your target DHW temperature, keeping the boiler in condensing mode even during DHW production. The small coil issue is confined to the North American market. The Euro's have had LARGE coils in their indirects for many years.

Used them for many years in multifamily dwellings with excellent results. Pricy, yes, but if peak efficiency is your ultimate goal, then price shouldn't matter. People who utilize solar thermal aren't doing it for the return on the investment. they are doing it for the conservation effort.

ME

SWEI

ced48 said:

How can you heat water to 130 degrees or higher, and keep a condensing boiler always condensing?

Easy when the incoming water is less than 70°F, as long as the HX has enough area (and hopefully is a counterflow design.)

njtommy

The turbomax is pretty crazy.

JohnNY

Hey @Mark Eatherton
Are Turbomax and Ergomax related? It looks like very similar technology to me and I've had great results with latter.

Mark Eatherton

John, I THINK they may come out of the same factory in Belgium, but I honestly do not know. They are identical in applications, but not sure if surface areas etc. are equal. Turbomax seems to me to be the better, and pricier of the two. I use to know the woman who introduce this concept to the US, but have not heard from her in many years. The ONLY caution I'd make in general, is to be aware of water quality issues (hard scale precipitation) and if need be, apply some sort of water conditioner to avoid lime scale accumulation. Here in Denver, we run 7 grains, and I have NEVER had one lime up on me. Operating at the lowest temperature possible is one way to negate the accumulation. Although their spec's are based on 180 degree F entering water, in the real world, they do not need that hot of water to perform well.

To anyone reading this thread, if you are confined to having to use the large tank, small heat exchangers typically used here in N.A., why not consider adding a large flat plate HX to the boiler return, running the boiler return water through the A side, and the incoming cold DHW into the B side, thereby preheating all entering water into the crappy tank, and lowering the entering boiler water temperature. It's all about heat exchange surface area, and it you can't get it fit into the tank, you can do it externally, at a price... I've actually had my own DHW temporarily provided by a 50 K Munchy through a FPHX and it worked great under continuous load. Not a good idea for hand washing, dish washing etc, but when it gets locked into a long load (showering) it works fantastic and keeps the con happening in the modcon. And we had a virtually endless supply of hot water.

I have since upgraded to a 119 gallon solar pre heat, and an 80 gallon aux (wife likes long hot baths, unwilling to wait 30 minutes to fill tub). Between the solar and the GFX Green FoX drain waste heat recovery heat exchanger, we use very little LP during the non space heating months. (This is my retirement home in the Colorado mountains) The GFX recovers about 50 to 60% of the energy that is normally lost down the drain. I do not understand why this isn't a minimum code requirement... And hopefully, some day it will be.

Food for thought.

ME

kcopp

Mark said...
"I have since upgraded to a 119 gallon solar pre heat, and an 80 gallon aux (wife likes long hot baths, unwilling to wait 30 minutes to fill tub). Between the solar and the GFX Green FoX drain waste heat recovery heat exchanger, we use very little LP during the non space heating months. (This is my retirement home in the Colorado mountains) The GFX recovers about 50 to 60% of the energy that is normally lost down the drain. I do not understand why this isn't a minimum code requirement... And hopefully, some day it will be."
----------------

Just installed one a couple months ago!
I insulated around it before the wall was closed up but they actually state you don't need to....

hot_rod

I have used one of the Caleffi tanks with the upper and lower coils series together. They are 1-1/2" coils and adding the two gives you about 60feet of HX coil. It is all about the HX surface area.

The two "max" companies were partners somehow and had a falling out and went separate ways, from what I remember. Jean used to hang out here, worked for ErgoMax. She knew the rest of the story.

I did have the opposite experience with a reverse indirect, as ME. I used one to buffer a waste oil Clean Burn boiler and provide DHW. Within 1 year the coil limed completely closed. But that boiler did have a tendency to run very hot, around 200F when they start to ash up inside. Also the Missouri water tends to be around 20 grains, or higher.

SWEI

hot rod said:

It is all about the HX surface area.

This ^^^

Solid_Fuel_Man

I have a Heta-Flo (branded as Oventrop) indirect with the two coils. Upper one is supposed to be for boiler and lower (larger) for solar. Very close approach temps.

SFM

Solid_Fuel_Man

Lotsa surface area and made in USA!

dtrani

I have a HTP 45-gal indirect set to 150 deg with 170 deg set point for DHW. It runs about 15 min to recover spending about 5 of those minutes in the condensing range. Not too bad. I think I get more time condensing for DHW than I do heating the house, but that's another story...

brnrman1

Simple answer Energy Kinetics Accel CS forget about having the coil in the tank use a plate with a 70 degree delta condense all day long...

NYplumber

Plus one for the turbomax. If water quality is good, the coil will stay clean. It works like an ondemand water heater, except theres no fire the heating medium is water. The coil stays clean when water velocity is high and like mark mentioned, water temp is low. I have a few in the field that are working well. At the bare minimum, if it doesnt condensate, it acts as a buffer.

Aaron_in_Maine

The Heat Flo high output indirects have double the heating coil of their regular model.