Heat pump customiztion

[vij36]

Dear All,

We have a typical requirement of large volume of hot water up to 20,000 liters and some confort cooling loads
We are planning to have a heat pump.

Could please let me know what are the design parameters for integrating heat exchanger (shell&tube) with an appropriate compressor for this kind of requirement. And the volve requirement for piping.

Should we have a double compressor since with a single compressor the maximum heat load achieved is only 58 degree as per many vendor quotes.

Heating load - 20,000 liters at 85 degree Celsius
Cooling load - 9 degree Celsius

Some times heating load may not be required like on weekends and vacations.

Thanks,

 

[Drazen]

Your post clearly shows that you need HVAC engineer in problem definition phase already. You need to understand thermal processes to be able to define your problem.

 

[LittleInch]

That is apparently the downside of a lot of the heat pump ideas, i.e. you need to use it for underfloor heating or use bigger radiators.

20,000 l at 85C - for what?

But agree you need to understand what is a practical limit and operation of a heat pump system.

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

 

[vij36]

Dear Sir,
We are a charitable organization providing mid day meals to children in india.
In very limited amount of time we need to cook large amounts of food, pack and transport. The food(rice) is cooked in hot water medium. So in order to reduce cooking time we need this much volume of high temperature hot water. Every 5 minutes saved has a lot of impact since some locations are very remote and lot of other factors such as food served hot, hygiene etc., are taken into account.

As of now we are using diesel fired boilers for steam generation and want to replace them slowly.

I am a technical volunteer for this organization. Found the heat pump a good idea but we are very tight on budget. There are MNC companies offering to achieve this temperature (with cascade compressor). I am looking for a vendor who can propose a economical option who can understand our requirements.

 

[Compositepro]

While it is possible to have a diesel powered heat pump, I assume the ones you are looking at are electric. In that case you could get more get more heat from the exhaust of your diesel generator than you will from your heat pump.

I believe that the logistics of cooking for large numbers of people have been pretty well worked out over the last century.

 

[vij36]

We intend to use electric heat pump. Attached a dwg which I made after some discussion with vendors.

 

[GT-EGR]

There’s a lot more to your diagram than the heat pump. To get your peak sizing requirement we’d have to know your worst case sizing scenario - and how all these interrelated components work together

Are you talking about recovering the heat from the condenser end via a water cooled loop that then brings the rejected heat to your 20,000 liter tank? This looks like a pretty complex arenagemt for someone just dipping their toes into hvac, where did this setup come from?

The only criteria comment I can help with is you need to pick a starting cold temp and an ending warm temp of your tank, and then decide how fast you need to makeup that temperature difference. The volume over time is your flow rate and the cold and hot temp is your delta T and you can use basic heat gain equators to get your BTU input required

 

[LittleInch]

vij36,

what you are doing is a noble thing and I wish you good luck.

however I think you've leapt into this without looking at either other alternatives or getting true data on what you're trying to do.

Ground source heat pumps can yield good efficiency in terms of energy in to heat out, but they are an expensive long term investment and probably not suited for your needs.

India being the warm place it is you are probably much better using an air heat pump or as your diagram shows, using the cold side to cool things.

Using a heavily insulated hot water storage tank would also be better.

But first look at what you have and see if there are smaller cheaper ways to improve the efficiency of what you have or perhaps add a few Solar water heaters to get the incoming water up to a higher initial temperature.

There are many lower tech cheaper things to do first, especially if your funds are low.

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

 

[vij36]

How about the product described in the attached file. It says very high temperature water heat pump. Mitsubishi product. COP is 4.

 

[Drazen]

Again, such ideas make sense only if they are based on deep understanding of thermodynamics, and this is what is entirely missing here, apparently, and the fact that you volunteer to charitable organisation makes things even worse if you would burn money into something complex, sophisticated, that needs to be fully elaborated before any financial commitment.

Why would you in any way think that it is good idea to use waste heat of heat pump to heat large quantity of hot water, quickly? I assume that media in your country is bombarding wider population with stupidities that advocate how any usage of renewables is good idea "saves energy and money" etc.

Delivering large amount of heat at high temperature is the last thing heat pump does - heat pumps works the most effectively when rejecting heat with highest possible temperature difference. If some typical condensing temperature for ordinary heat pumps is 50 deg. C, works with 15 delta T (vs. 35 deg. C of ambient), and you would need at least 100 deg. C on lower side of your cycle to be able to heat your water to 85 deg. C (the most favourable condition, very hard to be attained in practice), than you would need something like 115 deg. C condensing temperature - you would need very special heat pump.

Did your friend who delivers heat pumps mention it to you, and if he didn't, how it's possible if he is professional heat pump tech. support?

These only some of the issues and there are many others, which would make book of this post, but there is one simple point - you cannot have good ideas in thermodynamics without profound knowledge of thermodynamics.

 

[LittleInch]

Yes, but I'm pretty sure that when you look closely all the times it says up to 78C, it then adds ( when water leaving the evaporator at 40C)

Section 6.1 makes it clear in note 1
Plant side 70/78, source side 45/40 (in/out)

Now I know it is pretty hot in India, but 1m below ground temperature doesn't get to 45C.

So in fact this unit operates like most others - raises the temperature from the ground to the delivery by 30 to 35 C.

So unless you have a source of water at 45 C, you're not going to get 78C.

If you have a large area where you can solar heat water you might get there on a sunny day, but not from ground temperature you won't.

It's not clear what happens when the temperature drops below 45C in, but it seems likely that the COP will go down if you want to try to maintain 78C out.

You can't beat physics. Many have tried and many failed....


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

 

[lilliput1]

Why not just cook rice in a pot of water on gas fired stove burner? Gas is cheaper than electricity. Get rid of steam boilers. Use geothermal heat pump for space heating and cooling only.

 

[willard3]

Using a heat pump for your stated use is bad angineering; a gas flamer ans a pot is waaaayyyyy more efficient.

A heat pump is a carnot cycle with a maximum efficiency in the low 30% range. Heat pumps work best when delta T is very low, not what you have described.

 

[GerardNavarrete]

I think one can also go for the electric heater that is available in a smaller size. It is also capable of handling a large amount of water. We just need to deep it.

 

[Artisi]

vij36, why not contact the Indian army catering dept. and ask how they prepare large amount of rice for their troops, sounds to me you are trying to re-invent the wheel.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)