Efficiency of an indirect water heater

jesmed1

https://forum.heatinghelp.com/discussion/comment/1825232#Comment_1825232

OK, thanks Matt. This is an old building with a number of potential air leak paths, so it's hard to say for sure where the worst leakage is happening. But one plus is that the first floor is concrete block construction with an exterior stucco coat that extends down below the sill plate onto the poured concrete foundation, so there is no air leak path through the sill plate.

I have read comments from people who have installed automatic vent dampers on their boiler flues, who said that their basements were always cold before they installed the dampers, and after the dampers their basements were warm. I don't know if we'll get the same result, but I'm willing to spend $300 on a damper to try.

Teemok

The effectiveness of heat transfer method topic seems to have taken over from the original indirect tank bash. My apologies. Flat plates are great, no doubt. Why has this become the topic? The recovery rate of a decent bottom coil indirect is more than adequate for most applications. Is the concern about the drop in transfer rate as tank set-point is approached? Who cares when the tank has plenty of hot water in stock at the top? I've cut open a few very old indirect tanks and yes there's some scale on the coil but most surface area was not. Maybe that's my areas decent water. I thought the HX tubing expansion tends to shed scale. The F. plate tank stirring might be a negative when operating at low tank temps. What's the priority of the problem? Engineering is a game of compromise. There nothing fantastic about an indirect nor is there anything very bad.

hot_rod

Ok, here is a sizing with the lower boiler SWT, 140 SWT, 125 RWT keeping the boiler condensing. Providing 120° DHW at a 2.8 gpm rate with a 100,000 boiler input. 38 plate 4.65 sq ft.

I don't consider 4 sq feet of HX surface big? Compared to the 40 sq. ft in the tank in tank?

I'm using the Smart 60 spec which shows 24 sq. ft? Looks like you need a smart 120 to get 40 sq. ft?

I can't find that 130 SWT spec on the tank in tank performance sheet, the lowest boiler supply they show is 160°. I doubt you are generating 2 gpm continuously at 120° with 130 boiler supply ?

Recovery vs instantaneous production is an apples to orange comparison.

I have nothing against indirect of any breed or brand. My point continues to be the flow on both sides will always beat heat exchange into a tank of still water

I think TT makes pool exchangers, how well do they work with to pool flowing through them? It's a mini indirect after all.

How about this compromise

Screenshot 2024-12-06 at 5.05.25 PM.png

Screenshot 2024-12-06 at 4.10.22 PM.png

Doug_7

Heating Efficiency is very important and holds huge potential to reduce operating costs and address climate change. You can argue technical details until the cows come home, but this gets very frustrating. At some point it is the bottom-line financial-results that are important.

We have 3 nearly identical sister condo buildings. The other two buildings are all original equipment - natural-draft boilers, direct-fired DWW tanks, over-sized hallway ventilation systems, driveway snow-melting-systems etc. We are the only building that has replaced all this original, inefficient equipment with high-efficiency ModCon's, Indirect DHW, and correctly sized ventilation etc. and we set it up for high-efficiency operation, about 15 years ago.

I recently visited these two buildings and their Heating Control Settings are set by the heating technicians to avoid any no-heat complaints from residents. For example the building heating boilers for these two buildings is ON 24 / 365 whenever the outdoor temperature in below 70º F and their heating pumps run 24 / 365 regardless of the outdoor temperature.

Our building heating is only ON when a suite Thermostat actually calls for heat. Suites don't actually call for heat very often, because of the thermostat dead-band, so our building heating boilers and pumps only run about 1/3 of the time over a year. Proper controls will greatly improve efficiency, and save an enormous amount of money over the year.

I read the natural gas meters of all three buildings once per month. Our building gas use is exactly half that of the other buildings - summer and winter, year after year. Their Electricity use is even worse, but that is another story.

The other two buildings know this, but they are very set in their ways, very resistant to change. They simply do not understand anything technical and it sounds like a lot of work to them. After all - their gas bills have always been about the same - high.

Not sure why I decided to tell you this. Just frustrated I guess. Technical points are something we should all be able to easily and quickly agree on - it is just Physics after all - the laws of nature.

Not sure why it has to be so hard on this website, to agree on simple, important points, which would help others to make their heating systems much more energy-efficient, and save a lot of money in the process. The potential is huge.

Doug

hot_rod

https://forum.heatinghelp.com/discussion/comment/1825247#Comment_1825247

I started this post for those looking to maximize the efficiency of dhw production

Specifically those with mod cons, solar or heat pumps looking to use the lowest possible temperatures. Although it applies to any and all heat sources

To that point a heat exchanger with two forced flows beats a coil or a tank in a pool of still water, ie a typical indirect, by a large margin in fact.

Idronics 29 explains the theory, application, sizing examples pretty pictures and more

Pretty simple basic observation. Food for thought for thought for those willing to learn. Which is most of the HH membership😀

Or as my heat transfer guru explains it

IMG_9120.jpeg

Doug_7

I do not care anymore.

Doug

hot_rod

it applies to convectors also, fin tube compared to a kick space heater as an example

IMG_9121.jpeg

Teemok

@hot_rod HH beginners mistake, I didn't read it from the start. 🙄 Effectiveness makes more sense to me than efficiency. The effectiveness comes at a cost. thanks for clarifying.

Kaos

As a point of reference in the land of expensive energy, most European indirects use pumped plate heat exchangers.

From monitoring my DIY indirect, in the coil in tank setup the RWT temp was always pretty close to boiler temp. With the plate HX, the return is about 1C above tank temp. For my setup with a heat pump, that is a big difference in COP.