2 Heat Exchangers - Overkill?
 

To begin, I have a new Carrier model 50YDS049NCD311.
That's a re-badged Climatemaster 4 ton indoor split GSHP.

My project involves converting this system into a hydronic heat pump. The way I intend to do this is to build an enclosure on top of the existing unit which will house the following components:

1) 4-ton TXV (Sporlan CBBIZE-4-GA)
2) Filter Dryer (Sporlan Catch-All)
3) Sight Glass (Sporlan See-All)
4) 4-ton or larger heat exchanger(s)
5) circulation pump (will feed a water storage tank)


This week I came into a pair (two) of these TurboTec BTSSN-48 coaxial heat exchangers (see attached performance graphs).

Is there any downside to running two of these 4-ton rated heat exchangers in parallel?

Do I stand to gain much in efficiency or should I just run a single HX and save the other for a future project / shelf-spare?

Thanks. As I get going on this I'll start posting up some photos, etc of my project.

http://i776.photobucket.com/albums/y...pscu9bwrcf.jpg

Looks like a great project. Putting the two coaxial Hxs in parallel cuts the heat exchanger resistance in half. Good thing as a lot of the total system resistance is in those helical/spiral exchangers. Allows use of a smaller pump and less cost to run it.

Would get double the amount of BTUs from the incoming water stream.

Water tank?


Steve

Thanks, I was thinking the same things: less head-loss in the water circuit and double the wetted surface area in the HX = more efficiency.

Since you asked about the water tank... I plan to use a standard electric water heater tank with a few temp sensors. It will store the heated (or chilled) water produced by GSHP through these 4-ton HX.

From your post, I think I may have miscommunicated my setup in my original post...

The heat pump I have is a GSHP already. It has a pair of 2-ton Koax brand HX inside in parallel. These HX take the ground loop water and couple it to the refrigerant. This GSHP is only one half of the split system. It was designed for use with a fan coil unit in a forced-air sytem inside the home.

My building is set up for hydronic heating and cooling with radiant concrete floors and large radiators for chilled-water. So I want to use these 4-ton TurboTec HX to turn this split system GSHP into a packaged hydronic (water to water) GSHP. Hopefully that makes more sense.

Did you ever try this in an actual application TechShop?

I have brazed and pressure tested the heat pump but have not tested the system yet. I will be doing that over the next few weeks. Here's a thread with some details and photos of the system and the pump itself:

http://ecorenovator.org/forum/geothe...onversion.html

If this were true, then having 4 HXs in parallel would give you 4x the BTUs, and having 8 HXs in parallel would give you 8x the BTUs, etc. and eventually your BTU output would exceed the available heat energy.

Will not happen, violates the laws of physics.

When you run 2 HXs in parallel, you are reducing your resistance only because you are reducing the velocity of fluid flow through each HX.

Reducing the velocity reduces the BTU output.

You will have an increase in efficiency but nothing like 2X.

Sincerely,

-AC_Hacker

This is absolutely true. You cannot transfer more heat than what is available. What I am hoping for, at best, is a small increase in HX efficiency.

If I am moving 10 GPM of water through one heat exchanger, installing two will cut the flow down to about 5 GPM per heat exchanger (not accounting for head-loss). The water will be exposed longer (due to 1/2 the velocity) and thus it will reach a slightly higher temperature. As the water becomes hot, the heat will not be absorbed from the refrigerant as quickly because HX depends on a substantial Delta-T.

In a perfect world, double the surface area per given quantity of water combined with water moving at a lower velocity means that the Delta-T in the system should be slightly less than a single HX. That combined with the fact that the same quantity of water is flowing with less head-loss may net a tiny increase in system efficiency.

I will not have a control for this experiment, I have never run this system with a single heat exchanger and most likely never will. That means ultimately any data I collect will be meaningless in terms of comparison of 1 vs 2 heat exchangers.

I started this thread to see if anyone had any good input on why NOT to build the system this way.

The only negative aspect I could come up with on my own was fouling. If the water velocity is too low to create turbulent flow in the HX, it could cause excess fouling. I decided that since this is the heated side of a closed loop system, I shouldn't have any major fouling issues provided that I use clean distilled water and the proper anti-freeze / coolant mix. Furthermore, I have selected a pump that should maintain flow through each HX that is well within the manufacturer's design envelope.

I believe even if you only ran one of those turbotec units, the unit would have a greater COP versus running an air handler. By running two, you should extract even more btu's per watt of compressor power. If the turbotecs are too effective, you may not develop enough head pressure unless you choke the indoor water flow. That's what trials are for.

That's my expectation... I will be running the system with some PLCs, so I will be doing lots of trials to tune it for good efficiency.