Anyone Ever Use a Flat Plate Heat Exchanger?

As the topic asks, has anyone ever used a flat plate heat exchanger?

I've seen them in those huge outdoor wood boilers. From what homework I've done a 70 plate exchanger will heat a WELL INSULATED 3k to 4k sq. ft. house.

Well, my house is over 100 years old so I may need one with more plates

Basically, I'm just looking for comments/opinions on these kinds of heat exchangers.

Heat exchangers are used with outdoor woodboilers since the wood boiler is usually an "open" sysem that you want to keep separate from the pressurized system in the house; or as a means of tying the wood boiler into a hot air system. As for your question about the size, sizing the heat exchanger based on the size of the home really isn't the correct way to do it. One 3000 sq.ft home could have twice the amount of heat loss as another, and require a much larger heat exchanger. Your 100 year old house is probably in the second catagory

Ideally you would want to do a heat loss calculation on the house and go from there...but if you have an existing system that is adequate for heating the home you can base the heat exchanger size on the rated output of the current setup.

Are you looking at a water to air heat exchanger or a water to water heat exchanger?

Plate and frame heat exchangers are the most efficient style.

markviii wrote:Heat exchangers are used with outdoor woodboilers since the wood boiler is usually an "open" sysem that you want to keep separate from the pressurized system in the house; or as a means of tying the wood boiler into a hot air system. As for your question about the size, sizing the heat exchanger based on the size of the home really isn't the correct way to do it. One 3000 sq.ft home could have twice the amount of heat loss as another, and require a much larger heat exchanger. Your 100 year old house is probably in the second catagory

Ideally you would want to do a heat loss calculation on the house and go from there...but if you have an existing system that is adequate for heating the home you can base the heat exchanger size on the rated output of the current setup.

Are you looking at a water to air heat exchanger or a water to water heat exchanger?

Hahaha, yes my house is definitely in the second category

I am looking to do an air to water exchange. This is where my lack on knowledge comes into play. Before yesterday I've never heard of a plate heat exchanger. I have a series of coils in my stove now which do work but I'm tinkering and I'm thinking of revamping my stove setup.

1. the plate exchanges are smaller and seem easier to work with.
2. I'm not 100% sure that they'll work like I'm hoping they will

Here's a site I've found the explain them a bit... but I just don't see how something so small could be so effective?
http://www.dhtnet.com/brazed_plate_heat_exchangers.htm

A plate exchanger is a water/water exchanger, not a water/air exchanger..

I use a plate exchanger to tranfer the heat from my coal boiler in an outbuilding to my baseboard hotwater heating system in the house.. I also use a smaller plate exchanger to heat my DHW. [domestic hot water].

The Plate exchangers are VERY efficient at transfering heat, I haven't heard of any problems with them, mine are brazed SS. The passageways are small, so I suppose an exchanger could get plugged with sediment or crap in the water.

Greg L

JJLL wrote:Here's a site I've found the explain them a bit... but I just don't see how something so small could be so effective?

To answer your question: proportionate to the water volume and heat quantity, there is lots and lots of conductive surface area to spread that heat across, in a relatively compact, low-loss configuration enabling a quick and efficient transfer of heat.

http://flatplateselect.com/site/pub/login.aspx?Re ... odels.aspx

This website has a very nice fphe sizing calculator that you can use for free if you sign up. They want a company affiliation and email address among the usual info. I used my business name and type straightforward; an unrelated business. I never have gotten any emails or solicitations. I can sign on and use it anytime. It is technical but after some study of the inputs and desired outputs you will get the proper size heat exchanger required. You will need to know your heat loss.

Plan on using a strainer because the fphe's can plug up otherwise, especially with an open system.

You can't really get one too big but you can get one too small. Since they are pricey, it will pay to get the right one. Shell and tube exchangers are great for large volumes and less likely to plug; Pricier though and less efficient. If you are using wood, efficiency may not be a issue in the selection between fphe or shell and tube designs as long as the required heat volume is transferred.

Hey guys, thanks for all the advice and links, they're definitely helpful.

Greg, let me ask you, if you had an indoor boiler/stove I'm assuming the same effect could be achieved?

Like you, I would like to heat my baseboards and a few radiators using a flat plate exchanger. I'm just afraid of spending a few hundred dollars and drilling a few holes in my stove only to learn the the thing melts or doesn't work.

Using one in your outdoor boiler then running it into your home keeps your house at a comfortable level? How many plates do you have in your exchanger?

Again, thanks guys for all the help.

JJLL wrote:I'm just afraid of spending a few hundred dollars and drilling a few holes in my stove only to learn the the thing melts or doesn't work.

Stove? That won't work, you need a boiler.

coaledsweat wrote:

JJLL wrote:I'm just afraid of spending a few hundred dollars and drilling a few holes in my stove only to learn the the thing melts or doesn't work.

Stove? That won't work, you need a boiler.

Perhaps this is my problem. My stove is literally 3 feet away from my boiler. I was thinking of putting the plate exchanger in the stove, then run that into the boiler.

Basically, I can move the hot water through my system already, I've get a few water coils inside the stove that do produce a good bit of heat, I'm simply looking to get more heat. I'm currently using the aquastat and the pump from my boiler to circulate the water. The water flows fine. I'm just looking for more heat.

The funny thing is, the colder it gets outside the more I become focused on this idea

JJLL wrote:Perhaps this is my problem. My stove is literally 3 feet away from my boiler. I was thinking of putting the plate exchanger in the stove, then run that into the boiler.

Stove, did you say stove?
Get a boiler and you won't need a heat exchanger, what you describe will not be an effective solution. Plate heat exchangers are used in water to water heat transfer only.

I agree with coaledsweat, putting a plate exchanger inside a stove to collect heat will not work.. you need as much surface area inside a firebox as possible to collect and transfer heat to the circulated water..

Get a boiler,, it is designed to heat water. A plate exchanger is designed to tranfer heat from water to water without mixing the water.

Forum member smitty intalled two SS coils in series in a big handfed stove, but you I believe have a stoker stove,, this produces a lot less heat .. A boiler designed to heat water is best..

My plate exchanger is a 40 plate, the DHW exchanger is a 30 plate.

Greg L

Greg:
The plate heat exchanger in the firebox idea sounds like an interesting option to the stainless steel coils. I looked at the link posted earlier and it says that they use copper or nickle brazing to make these plate heat exchangers. I wonder how that would hold up to the firebox flame temperatures without it leaking? I also wonder how you would calculate the approximate heat exchange of such an installation? Other than using a boiler, it maybe better to fabricate your own firebox tank. I saw these tanks for sale at the Ohio Amish Lehman's Hardware Store catalog http://www.lehmans.com "Hot Water from Your Wood Stove" they sell. It is only a box about 6" x 12" x 2" made out of 1/4" plate steel lined with a high temperature Teflon coating inside. They call them "The Thermo-Front internal hot water heater." DOUG

DOUG wrote:The plate heat exchanger in the firebox idea sounds like an interesting option to the stainless steel coils.

The problem with it is that a plate exchanger is designed to transfer heat from one liquid medium to another inside of itself, not from external air to it's internal medium. It will do a very poor job of putting heat from a firebox into water. You would be better served with a coil and SPEND A LOT LESS MONEY!

Hey guys,
Thanks again for all the advice. Being a guy who tinkers I always appreciate good input.

DOUG, if they weren't so expensive I'd give it a shot, but after what I've read here the only idea I could see "possibly" working would be to keep one of the loops in the exchange open so that hot air can enter it. But I believe heat transfers between liquids is better/faster than air to liquid transfers.

For now, its back to the drawing board... or to the showroom to look for a boiler

Thanks again!

If you measure the square inches of the outside of a plate exchanger, you will see that the 'box' really doesn't have that much surface area,, about the same as a single 'coil' from HilKoil.
I really don't know if the plate exchanger would hold up to the heat or the corrosive environment in a stove,, but I really doubt it.. I'd stick with SS tube for a heat exchanger..
Several forum members have made custom heat exchanger coils for their stoves.. and have had success with them.. you might want to consider getting a welding shop to fabricate a coil for your stove.. or use a pair of ready-made ones..

But beware that a coil in a stove is really meant for the slow and steady heating of DHW, not to heat a house or a boiler.. There just isn't enough surface area heated by the fire on a coil.. A coil can heat 40-50 gallons of water overnight or during the day when there is no call for DHW. But a steady draw of heat for baseboard or radiators needs a boiler for fast recovery.

Greg L