heat pump for cooling condenser and boiling mash

[hefezelle]

Short version:
Has anyone used a single heat pump to both cool the condenser and boil the mash? It seems this should be vastly more energy efficient, and decrease cooling water consumption as well as electricity/gas/wood consumption.

To elaborate:
For both ethanol and water it takes about five times as much energy to vaporize (assuming the liquid is already at boiling temperature) as it takes to warm the liquid up from 0°C (32°F) to said boiling point. That means when running a still the biggest chunk of energy isn't used for warming up the load, but for introducing a phase change from liquid to gas in the boiler. This evaporation happens at a fairly constant temperature range (some degrees blow boiling point of water for a mash, or some degrees above the boiling point of ethanol for low wines).

The same amount of energy used for evaporation is given off by the steam as it condenses into a liquid, which again happens at a narrow range of temperatures, but at a somewhat higher temperture than in the boiler. Now, instead of discarding the heat given off at the condenser and introducing new energy to the system in the boiler, how about using a heat pump to transfer the heat from the condenser down into the boiler, "reusing" it so-to-speak?

One would need a heat pump designed to operate at that temerature range (ca 70°C/160°F on the "evaporator" side and ca 110°C/230°F on the "codenser" side of the heat pump cycle), which sadly implies you can't just use a fridge cooling cycle. I guess you would still need some additional heating of the boiler, even if the mash were already close to boiling point at the beginning of running the still - but in theory it should be significantly less than in a conventional setup.

It seems that other people have had the same idea, or at least a similar one before, but since the configuration mentioned in that thread is somewhat different than what i was thinking of (i guess, not entirely sure there), i decided to put this into a separate place. Also, there was never any conclusive answer in that old thread.

Please chime in if you spot something i haven't thought of, and tell about it if you have first hand experience!

[Wild Bill]

That would be one tricky one off design with huge surface area heat exchangers. Not practical unless you are a very sharp hvac guy with access to free/low cost parts and way too much time on your hands.

[Kareltje]

Sehr geehrter Herr Hefezelle,
Wir können uns richtig freuen mit Ihrer Beiträgen!

Using the heat of condensing vapour is already practised by cognac-distillers.
Speaking for myself: I sometimes use the heat of the backset to dissolve sugar for the next batch of rum or grain ferment.

If I remember correctly, NZChris has made some constructions to reuse heat, but in New Zealand distilling is legal.

You bring up a very interesting subject.

[cede]

I studied a bit heat transfer when I was working on new types of wells for heat pumps, and we had a 2 stages heat pump, I mean 2 chained compressors using 2 different gases.
It was a real pain to setup but worked well and finally the wells were so efficient that earth was not able to provide enough heat in a small time.
Anyway, heat pumps are good when operating in a certain temperature range. Their efficiency can be great. But as soon as you go outside the zone, the efficiency decreases badly and you're better to heat using conventional methods.

As said Kareijte, you can reuse some heat that would be lost, but I doubt an hvac setup would permit to condense on one side and boil on the other.

[hefezelle]

Sehr geehrter Herr Hefezelle,
Wir können uns richtig freuen mit Ihrer Beiträgen!

Aww thank you, much appreciated, really!

Anyway, heat pumps are good when operating in a certain temperature range. Their efficiency can be great. But as soon as you go outside the zone, the efficiency decreases badly and you're better to heat using conventional methods.

I think the temperature in the still condenser will always be fairly close to the evaporation point of ethanol, if you're running a reflux still. The boiling point of what's in the boiler will increase, but not by a huge margin. So in my mind the temperature ranges are pretty well defined, with the one exception of a big gap between the boiling points of load during a stripping run vs load during a sprits run. Am i mistaken here?

I studied a bit heat transfer when I was working on new types of wells for heat pumps, and we had a 2 stages heat pump, I mean 2 chained compressors using 2 different gases.

What refrigerants did you use? What was the envisioned temperature at the second compressor stage? Do you have suggestions as to what refrigerant should be used in the setup i proposed?

[Kareltje]

I once thought about the use of Peltier-elements, but a quick scan did not encourage further study.

But it is interesting: I would love to hear more about it.

[cede]

What refrigerants did you use? What was the envisioned temperature at the second compressor stage? Do you have suggestions as to what refrigerant should be used in the setup i proposed?

On top of my head it was R410a and R22. I was not the one who played with the gases.
I was interested in understanding what was going on inside the box as I was doing the electronics to drive the compressors among other things.
I had to closely monitor pressure and temps to stay into the points on enthalpy charts the hvac guy wanted

[Wild Bill]

While it is a neat idea I think you would be better served trying to conserve energy and resources in other ways. For example I discharge my liebig into my hot lauter tun holding 20 gallons of water. That in turn flows into my mash tun holding 20 gallons as well which is then pumped to the inlet of the liebig. On a 12 gallon still run the water temp will raise 50 degrees in each vessel. I will then start a new mash for beer or spirits with this water and not use as much propane and no water is not utilized. Many ways to save if you put your mind to it.