Flat plate for DHW

Bob_115

What size Flat plate heat exchanger do I need to provide DHW at 2 gallons per minute if the boiler is set at 160 degrees? I intend to use a circulator and 3/4 inch copper on the supply side . The output side is 1/2 inch copper.

hot_rod

You need to know boiler gpm flow and incoming water temperature and final temperature 

There are a bunch of free online sizers. They usually spit  out a few size options 

The plate HX in combi boilers are small, maybe 3x8 10 plate. No harm in over sizing a bit.

Bob_115

Incoming water temperature is 50 degrees . Do you know where these calculators are specifically? I think boiler supply through a 3/4 inch copper line powered by a taco 7 circulator would be 4 gallons per minute.

Robert_25

Bob, I have a 5x12 20 plate served with 3/4" pex and 160 degree boiler water. Flow through boiler side is about 3 gpm. Paired with a 50 gallon storage tank it easily provides all the DHW for our family of 4.

If you are not using any kind of storage, I think you would likely need a 30 plate to make up for the "low" boiler water temperature. Most of the ratings for plate HX in DHW application is based on 180-200F boiler water.

Take a look at the charts: https://s3.amazonaws.com/s3.supplyhouse.com/product_files/BP400-30LP-Selection-Guide.pdf

mattmia2

B&G has a calculator as well as several others. Make sure your flow and delta t numbers are realistic, you can put anything in but it might not be what your system will provide.

MikeAmann

@Bob_115
Are you assuming that you can get 2 gal/min of continuous hot water WITHOUT a storage tank?

hot_rod

Everything you ever wanted to know about heat exchangers here
https://www.caleffi.com/sites/default/files/file/idronics_29_na.pdf

You can do the calculation longhand, or use the software as the demo shows in this journal.

Or guesstimate based on what is commonly used. The more HX surface the quicker the exchange and also the lower the A
side temperature can run

On my last shop I could generate 110 outlet with only 120 on the A side supply. To get continuous 2 gpm at those conditions required a 5X12 - 30 plate exchanger.

The numbers can be manipulated a dozen ways, you need a few entries of stable  or known date, start with the temperature you can supply, and the final gpm and flow rate you want. The software or manual math will solve the equasion 

Bob_115

Thanks to all who responded. I will plug in the numbers to see what is required. I think the 5x12 30 plate would be the right choice as I don't have a lot of room for a storage tank.

hot_rod

What size boiler do you have? That will be the determine factor on how much DHW you can generate, and how quickly 

A 120 Combi boiler as an example could give you a continuous 2 gpm with 50f incoming, 120f outlet. A typical 70 degree rise that most use for performance ratings.

If you have a smaller output boiler, adding a tank would allow you to store some DHW, generated at a slower rate. 

So it really comes down to what you want or expect for DHW capacity.  The engine (boiler) driving it will be the final answer to what is possible

Many families  get by with a 40 or 50 gallon tank, about 35,000 btu/hr. It may take an hour to recover depending on how low of a temperature you pull down to. Around 103f us where the shower may start to feel too cool.