Water to air heat exchanger used as a hydronic emitter?

Pulse

Wouldn't a water to air heat exchanger used as an emitter push out some major BTUs compared to baseboard/panel radiators?

I know they are not that pretty, but they are fairly cheap. You can get a 16"x18" water to air HE @ ~$150 and a Myson 16"x24" panel rad @ ~$150. The panel rad would give you around 1300-1800 BTUs @ 140 SWT(depending on thickness). I would imagine these water to air HE offer much greater BTU output.

This may be foolish, but if not, it sounds like a nice idea for garages and similar areas.

mattmia2

It is usually called a unit heater depending on exact form factor. they are common in industrial installations.

hot_rod

Called forced convection when you add a fan or air movement.

In a shop they work well for a fast start up, melting ice and snow off vehicles. Downside are noise, they blow dust or whatever is in the air, and hot air stratifies at the ceiling.
I have seen homemade ones from car or truck radiators with a simple box fan behind them.

Pulse

@mattmia2
@hot_rod

What if they were used without the fans. They are already sold with steel frames. Attach some steel sheets to the sides and wouldn't you have yourself a nice little convention/radiant heater that produced a much better BTU to cash ratio than anything that currently exists on the market?

EBEBRATT-Ed

Anything you pump water through that has some heating surface will give off heat. You can run bare pipe in a bunch of loops. They did this in the old days for steam heat

GroundUp

We install them all the time. Without the fan, the heat output is very minimal.

Pulse

GroundUp said:

We install them all the time. Without the fan, the heat output is very minimal.

I find that hard to believe. Something similar to what is pictured above should out preform anything that is currently on the market(e.g panel rads/baseboard).

Matt_67

It’s not a ton of heat without a fan. Many commercial/industrial buildings have unit heaters where the coil flows all the time and the controls cycle the fan to maintain space temperature.

mattmia2

Pulse said:

@mattmia2
@hot_rod

What if they were used without the fans. They are already sold with steel frames. Attach some steel sheets to the sides and wouldn't you have yourself a nice little convention/radiant heater that produced a much better BTU to cash ratio than anything that currently exists on the market?

Without the forced air there would be little output, it would have output similar to a similar sized panel radiator. Mass market european radiators are quite inexpensive. Commercial unit heaters and coils tend to be fairy pricey.

It is also common in large buildings to dehumidify and chill air to about 55 f and distribute it throughout the building and put hot water or steam reheat coils in the ductwork at individual rooms.

Pulse

I do not understand how an all steel panel radiator can perform just as well as this copper/aluminum panel.

Look at Smith's HE2 or other baseboards that increase copper/aluminum fins. Doing so provides them ~ 100 BTU++ more per foot over your average baseboard.

If a company built a panel radiator that had internals like this water to air HE, It would be a beast and better than anything out there.

hot_rod

Put a piece of cardboard in front of your car radiator and see the difference between forced and natural convection 😉

possibly a bit better output from a slab coil if mounted on its side to allow cool air to rise up thru the fins, 

JUGHNE

Yes, a slab on it's side and then a sheet metal box around it for gravity chimney effect.....the taller the better......more air flow with height.

However the closely spaced fins as shown in your picture above will slow the air flow....that is made for forced air.
Look at the fin spacing in a standard gravity air convector.

jumper

Maybe if you mount a car radiator almost horizontally with steam or very hot water?

Zman

I did some data logging on unit heaters a while back. They emit about 10% of their rated capacity when the fan is off.

JUGHNE

I know of a very handy guy who has a wood burning boiler outside and a car radiator in his living room with a fan behind it.
He is quite a "rustic" dude......never married BTW.

EdTheHeaterMan

@Pulse
Heat travels in 3 ways
1. Conduction
2. Convection
3. Radiation
You need the heated water in the emitter to do all of the above as much as possible and as efficiently as possible. Some engineers, with more degrees than me, sit at drafting tables and computers with CAD programs to make the decisions that you are asking about.

Basically for your "garage or other areas like that" where the aesthetics are not important, the more efficient may very well be able to work better than a panel or baseboard. for those to work, you need airflow across the emitter. To get that airflow baseboards are designed to be installed near the floor where the colder air stratifies because it is denser (heaver).
That cover on the front creates a duct, or channel, or chimney-like effect causing the warmer air to exit the top of the emitter. this accelerates based on the temperature difference of the water. Without the front cover, the emitter can loose up to 85% of the rated value of the emitter. Test it out the next below 20°F day. Your home will get very cold the boiler will cycle on the high limit and your fuel consumption will increase.

In order to get your 16 x 18 HE to outperform the baseboard, you need to have the airflow increased to the point that the water temperature drops by about 15 to 25 degrees while it travels thru the emitter. If you don't want to add the recommended fan, you need a really good "Chimney Effect" (like 30 feet or so) for the air to remove enough heat. That would put all the heat in the ceiling where it will do little to keep you warm on the floor.

You are doing some good thinking. there are many concepts that make sense to me that later were proven incorrect by trial and error, reading, or teaching by someone smarter than me.

Keep thinking, keep questioning, and keep learning

GroundUp

Pulse said:

GroundUp said:

We install them all the time. Without the fan, the heat output is very minimal.

I find that hard to believe. Something similar to what is pictured above should out preform anything that is currently on the market(e.g panel rads/baseboard).

With a fan behind it to move the heat, sure. Just sitting there, no. A 16x18 W2A HX like you've got pictured with 180 degree water passing through it will put out approximately 2000 BTU in a 60 degree space. If you turned it on the side for some convection to work like baseboard that may very well raise output considerably, but the fins will also be routinely full of dust and crap in most spaces which drops the output back to minimal. Now add a fan and you're immediately 30,000+. Water to air heat exchangers are not new technology, no need to reinvent the wheel here.

Pulse

I understand now that air movement is required. The aluminum fins on these water to air HEers are definitely more dense, as much as 3x more fins per foot.

My question should have been why companies are not combining baseboard copper/aluminum fins into panel radiator form.

mattmia2

Pulse said:

I understand now that air movement is required. The aluminum fins on these water to air HEers are definitely more dense, as much as 3x more fins per foot.

My question should have been why companies are not combining baseboard copper/aluminum fins into panel radiator form.

Many panel radiator designs have fins welded to the back. There are higher output designs that are deeper that have larger fins (and maybe a second panel of water tubes.)

Pulse

mattmia2 said:

Yes, but panel rads are all steel. I believe at least a switch from steel water tubes to copper water tubes would accomplish two things. No chance for rust in the system and a better transfer of heat to the steel. The bulk of the radiator will remain steel for low cost and heat retention.

Gunna start my own line of panel rads, who wants to invest?

hot_rod

There are people that spend a life time engineering fin coils for maximum performance. An AC condenser is an example where they have tried to maximize energy transfer.
The fin shape, size, metal thickness, type of crimps are all maximized. Inside the copper or aluminum tube are grooves, rifling, for turbulators to get maximum turbulent condition, which are all part of maximizing a coils performance.

Visit the ISH show sometime, there must be thousands of radiator manufacturers that display every radiator design possible.

A kickspace heater is a classic example of how a small coil with a blower can get you a lot of Btu/hr in a small box.

With the goal of heating hydronically with SWT below 120F, there are some unique "enhancers" being designed for panel rads now.

Jaga radiator company has had a boost package out for years. I think Runtal now has a similar system to add on to panel rads.

jumper

Has anyone mentioned orientation of fins? Vertical enables convection.

EdTheHeaterMan

The orientation of fins is a big deal. and not just in airflow! I was once on a project where a boiler was designed to provide radiant floor heat (and snowmelt) for a car wash and also DHW for a laundromat. Somewhere there were braised plate heat exchangers installed 16 feet high above the ceiling to fill the water tanks. All the components were specified by the manufacturers' rep. design team. After 2 years of operation, the business owner was frustrated with the system not producing sufficient hot water to operate the laundromat.

I was called in to look at the waste oil burner on the project and everything looked fine and the workmanship was excellent. I suggested there was some mistake and the manufacturer's rep who specific the job should be called in. Later that year I found the braised plate heat exchanger was installed horizontal and it should be installed verticle. This oversite was missed by several professionals during the installation and subsequent service visits.

Wha ]t a difference a right angle can make!

BTW, The waste oil heater was operating great when I finished my part of the project.

mattmia2

Why was the hx's orientation an issue? was it unable to rid itself of air?

I think the size of the radiating surface has a lot more to do with the amount of heat a radiator can transfer than the difference in conductivity between copper, steel, and aluminum.

The heat excahngers designed for forced air are designed in general for a higher delta t at the surface than a radiator. The forced air will keep the temp of the air near the ambient, when you rely on convection and radiation, the air near the radiator will tend to be elevated above the ambient reducing transfer.

hot_rod

Yes you should avoid horizontal mount with connections facing down, there is no way to purge an air pocket out.