Noob Question: Using vapor refrigeration to heat water. Source is hot water around 90 C. 2

[Furious.George]

I have some software I wrote that I'd like to apply to heat moving/storage, for fun.

To that end, I've been studying the vapor compression cycle. This is complicated by the fact that I only have a general understanding of thermodynamics. The purpose of this post is put in writing what I think are reasonable expectations, in order to see if they are reasonable.

I want to extract heat from vessel with water/glycol @ 90 C, and put it in a vessel that is initially at 20 C.

If my understanding of the cycle is correct, which it probably is not, taking thermal energy from one side will increase the energy on the other by a similar amount, less the energy lost in transport. Efficiency will decrease as the destination vessel gets warmer. Once the condenser in destination vessel is at a similar temperature to the liquid in the same vessel, then heat transfer will stop. Depending on efficiency, this can be somewhere between 7 and 30 C of delta between evaporator and condenser.

Putting this all together, I should expect to reach an equilibrium where the heat loss from the entire system is equal to the input for my source water/glycol, and the delta between the condenser and evaporator is around 20 C. That might mean the source is at 70 C now, and the destination is at 90 C.

Does that sound right?

 

[LittleInch]

Draw this as a diagram please.

However it just sounds too theoretical and I can't see why you're bothering.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Furious.George]

LittleInch, thanks for the reply.

If I start with that, could we size the vessels such that the hot side is 90 C and the coefficient of performance is > 1?

 

[chicopee]

I believe that the diagram LI is mentioning entails more than what you have shown. Now you have to add the other half which are the heat exchangers and the associated storage tank with piping. In addition you have to have NUMBERS in all portions of the entire diagram. By number, I mean expected inlet and outlet temperatures, pressures, enthalpy and entropy values, and flow rates.
In your diagram, I see that the glycol/water solution at 20C in the evaporator will get much cooler as it heats the liquid refrigerant into slightly superheated state so thermodynamic properties have to be labeled for inlet and outlet conditions of the mixture in the evaporator and condenser. You will also need to show the Mollier diagram of the refrigerant for the entire compression cycle. In the Mollier diagram, the entropy values of the vapor compression cycle will be an indication if the path of the cycle makes sense. The glycol water mixture thermo. data may be commercially available so you'll have to do some research.
Before you go any further with your project, some retail stores such as either Lowes or Home depot have on the market hot water storage tanks heated by vapor compression system, so check those out. Now if you intent on completing your project, purchase a small air dehumidifier and cannibalize it to make a small prototype in your garage or basement but be careful by not damaging the coils.

 

[Furious.George]

chicopee, thanks for the tip on cannibalizing the dehumidifier, and water storage tanks.

I've done a bit more research, and am starting to wrap my mind around the project somewhat. As you suggest, when I get a better understanding, I'll make a diagram with humbers.