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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Aye.
The other thing that had become fairly clear was the need to minimise the hot water flow through the glycol heat exchangers.
This is so that the Q,in (based on Q,out + W,in -> source and compression respectively) results in the maximum temperature lift of the hot water.
I.e. 1.5MW in the condenser would result in a greater temp rise of a 180m3/hr stream, instead of say 210m3/hr.
The 3 PHEs are oversized so i think they would handle hotter water to bring glycol outlet temp up to its inlet temp (within reason). That make sense?
Finally - with a boosted hot water temperature, a new equilibrium would be established in the system, and undoubtedly the warm water out would be hotter. This has to be a good thing for a heat pump evaporator point surely? (temp lift smaller).
Best regards.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
It is a fine balance between energy and temperature,
why do you want to heat the water, you want to cool it!, you want to heat the glycol.
Remove as much heat as possible from the distillary water, directly into the glycol, then further reduce the water by refrigeration (lets say to 25C as required for the return), use HOR of the refrigeration plant to heat the glycol directly, we do comprimise the Heat pump COP, but have a greater amount of FREE energy.
Remember, think of the process as a whole, each loop effects other loops.
Only at the very final stages, can you look at specifics,
At the start you had very big loops, these now should be starting to reduce, to where an equalibrium is being reached in each loop, final control of the heat pump, finishes the loop balancing
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I recognise heating the glycol directly with refrigerant is the most efficent - but i was thinking about practical operation.
Incoming hot water is 1 line, if it was getting heated, would require 1 condenser., one control loop.
As is the 3 glycol loops are independant of one another (not fed from a main line), that would require 3 condensers (each with potentially different loads, (different radiator performances, etc).
Internal heat exchanger reconfiguration at the distillery is going on - hopefully this will boost the water temperature to the maltings by 2/3 degrees, and also work is being done to smooth out the flow pattern.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I understand, that your are looking now the practical application, which is good! I am unable to detrmine the correct design scenerio, without knowing the load profiles, thus total potential savings, which then limits the capital allocation, plus the physical limitations of the installation.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Just to confrirm Mad, when you talk about "load profiles" - this is the expected duties/range of variation on the condenser and evaporator?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Just to confrirm Mad, when you talk about "load profiles" - this is the expected duties/range of variation on the condenser and evaporator?
Not quite, it is load profile of the process(s) then indirectly the refrigeration limitations.
I believe this not just a case of adding a heat pump (and is the simplest option) to truely save while you have the oppotunity (without going overboard) focus on the whole.
You also need to look at things such as life of the system(s), for example if you had a single system/heat exchanger, how long to do you think it would take to get a replacement and what would be the cost of the plant not being in operation.
It is all about finding a balance, which is not as easy, as saying it.
You should have reasonable idea on a range of savings, thus a limits on a range capital expense,
You then start to move money around the different potential engineering solutions, and hopefully you reach a viable solution. (my gut feeling is you can do quite a lot) improved air heating, heat pump and control systems.
Mad
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Manny, you really do need to bite the bullet, fly MF over to see you & let him set you on the right path.
I see that he has been extremely kind in working around your technology probes, but, I must honestly say that you must both be very close to your respective IP boundaries.
Fairness should prevail at this point. Surely?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
desA
Manny, you really do need to bite the bullet, fly MF over to see you & let him set you on the right path.
I see that he has been extremely kind in working around your technology probes, but, I must honestly say that you must both be very close to your respective IP boundaries.
Fairness should prevail at this point. Surely?
I doubt Manny is in a position to sign off such a request on a purely theoretical study.They would need to be nearer to finalizing it for that to happen.There are such things as pictures, movies conferance calls Skype etc that will cover most things for now.
Plus I suspect someone would point out that using a company from the other side of the world would be fraught with difficulties with regard to accountablity and as such would assume they would prefer someone more 'local' ?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
^ Well, so said. It would be wonderful to have seen someone 'local' take the trouble to answer so patiently as has MF & with as much depth of experience.
My 2 pence worth, mind you.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
desA
^ Well, so said. It would be wonderful to have seen someone 'local' take the trouble to answer so patiently as has MF & with as much depth of experience.
My 2 pence worth, mind you.
I don't doubt MF's technical experience or ability. I just suspect a bean counter will have his input and question why they need to fly someone 1/2 way round the world. If that can be answered sufficiently then no doubt MF will get a BA ticket through the post at some point in the future. :D
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I appreciate your point desA, but as a student on placement I have no hope of securing cash to bring a consultant like Mad over. If I did then i would have when he was in the UK recently - and that would have been damn useful.
And Mad knows i am extremenly grateful for all his advice. I am now in a position where I can make rough estimates to economic potential, while baring in mind the whole process and operability of the heat pump thanks to his input.
Bartlett hit the nail on the head regarding my role to the company in this however. Getting a consultant in to look at the problem is a fair way down the line. The first stage is for me raise this to their attention and explain how it would work and what savings it could offer. And for this I need more than a basic explanation.
If it weren't for these wonderous forums & MF I would still be at stage one, on Excel trying to work out power of compression based on theoretical equations out of Perrys Handbook.
I.e. desA, I am far from taking the help for granted - but I have no weight to throw around $$$ wise.
Cheers
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
This thread is an interesting read. Keep it up everyone. :)
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
If and when this project becomes more than a study (which im sure in the future it will given carbon neutrality aspirations) I will be sure to ship over some 24yo cask str single malt, fear not.
Regarding your previous thoughts mad: if some of the heat pump kit were to fail or require maintenance, it would have little impact on the kilning process.
The system would switch to use exhaust air-to-glycol cycle as a means of pre-heating (for the down-time of repair your steam use - the primary heating - would ping up as this pre-heating is small compared to hot water use), however production would not be effected.
You would just have to burn X thousand more litres of fuel oil to compensate.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Hi, Manny did make it clear where his limitations lie (no worries there), always willing to accept a bit of Malt.
At some stage, a consulatant will be required. But before this is to happen, there is a need to prove a range of savings (which is what manny is doing), as far as an actual optimised designed process, no offfence given, manny does not yet have the experience (but does have the brains).
When you look at systems like this, you do need to visit site and get a "feeling" for the process. Something which is hard to do electroniclly.
As far as cost, it is not the cost, its the benefit. (as far local, earlier i did say it would via my UK sister company).
back to tech, manny you mis understand my point about service, most recovery systems do not effect the actual processes, only save money, but it is the cost in money terms when a recovery is off.
Thats why you look at multiple plants, with relativly standard equipment. (also it may help in the load diversity)
Focus on your load profile and then the savings, work on COPs of 4 for the heat pump (i know it could be better),
Mad
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I have been nudging with atoffe hammer, now lets use a sledge hammer, forget about the heat pump for now. imagine you have infinatively (can not spell) size air to glycol and glycol to water heat exchangers. Work out the theorectical savings, 100% for free.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Ok so the pre-heating radiators have infinate area, the glycol-water PHEs have infinite area.
Currently glycol can basically reach the hot water temps (oversized PHexchanger, excess of hot water).
Assuming we have an infinite size radiator (with excellent heat transfer coeff) and turbulent flow over the pipes&coils, air temp should be able to reach glycol temperature.
However the seasons come into this hypothetical: 0 degree winter air -> 50degC would save considerably more than 18degC summer air.
However: if we go with the average temp (10 C) and assume with an infinite sized radiator this can reach glycol temps of almost 50 C (air=25kg/s = 1MW).
Here glycol (13kg/s) would cool to ~29 C.
That is a lift of 40degC on the air. (from 10 to 50 C)
Currently, average lift observed is ~ 25 degC
Extra 15 degC approximately equates to £570,000.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Ok so the pre-heating radiators have infinate area, the glycol-water PHEs have infinite area.
Currently glycol can basically reach the hot water temps (oversized PHexchanger, excess of hot water).
Assuming we have an infinite size radiator (with excellent heat transfer coeff) and turbulent flow over the pipes&coils, air temp should be able to reach glycol temperature.
However the seasons come into this hypothetical: 0 degree winter air -> 50degC would save considerably more than 18degC summer air.
However: if we go with the average temp (10 C) and assume with an infinite sized radiator this can reach glycol temps of almost 50 C (air=25kg/s = 1MW).
Here glycol (13kg/s) would cool to ~29 C.
That is a lift of 40degC on the air. (from 10 to 50 C)
Currently, average lift observed is ~ 25 degC
Extra 15 degC approximately equates to £570,000.
I have not checked your numbers, so lets say that they are OK. 570,000 *3 years for reasonable payback, that is a s**t load of surface area, of course the theory is impossible, but you should by now understanding what I am talking about. Understand the process! Find the technical/capital compermise, then look at what energy is left, to be used by the heat pump, which can be used to heat the glycol, further increasing coli duty and thus air temp.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Radiators are copper tube, aluminium fin - and perform quite well from what i gather.
Obv. you will always have limited heat transfer across them as a function of heat transfer coefficients and pressure drop.
Observing the system, 1degC glycol increase results in a 1degC air increase (quite consistently)
Although 1degC glycol does not equal kW-wise 1degC air pre-heating, it performs this way.
So as a basis for calculation, i am assuming if you have glycol 5 degC hotter, air pre-heating is +5 degC.
This doesnt mean the glycol has 5 degC worth of heat taken out, however.
Perhaps when you are talking temps of 60-70, the radiators wont perform quite as well.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Radiators are copper tube, aluminium fin - and perform quite well from what i gather.
Obv. you will always have limited heat transfer across them as a function of heat transfer coefficients and pressure drop.
Observing the system, 1degC glycol increase results in a 1degC air increase (quite consistently)
Although 1degC glycol does not equal kW-wise 1degC air pre-heating, it performs this way.
So as a basis for calculation, i am assuming if you have glycol 5 degC hotter, air pre-heating is +5 degC.
This doesnt mean the glycol has 5 degC worth of heat taken out, however.
Perhaps when you are talking temps of 60-70, the radiators wont perform quite as well.
Your present system is wrong! so forget about it!
You have a million quid to design new heat exchangers (LOOKING AT SAVING 2/3 OF MAX POSSIBLE SAVING) this type of engineering is all about the money capital verses return.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
r.bartlett
I don't doubt MF's technical experience or ability. I just suspect a bean counter will have his input and question why they need to fly someone 1/2 way round the world. If that can be answered sufficiently then no doubt MF will get a BA ticket through the post at some point in the future. :D
If you want the best, you pay for the best;)
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I will have a good think about capital vs return then, and open up the concept of new exchangers / radiators, etc to see what would result in most efficient process.
I will get the managers drunk and get them to sign a contract for your concultancy eh
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
I will have a good think about capital vs return then, and open up the concept of new exchangers / radiators, etc to see what would result in most efficient process.
I will get the managers drunk and get them to sign a contract for your concultancy eh
Sounds like a good reason to get drunk, and that can not be all bad. lol
On system like this, the design evolves and that is OK
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Random heat pump question.
Is it the case the case that after compression the system condenser would just be one heat exchanger unit?
Or are there cases when it is more efficient to have a seperate de-superheater, condenser and subcooler in series?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Random heat pump question.
Is it the case the case that after compression the system condenser would just be one heat exchanger unit?
Or are there cases when it is more efficient to have a seperate de-superheater, condenser and subcooler in series?
Process specific!
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Very quick question here on Tuesday morning.
Clearly the latent heat of evaporating your refrigerant constitutes the bulk of the energy removal from your source.
But i presume your heat source would also sensibly heat it?
Approach temperature depending on the process and system of course :o?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Very quick question here on Tuesday morning.
Clearly the latent heat of evaporating your refrigerant constitutes the bulk of the energy removal from your source.
But i presume your heat source would also sensibly heat it?
Approach temperature depending on the process and system of course :o?
Superheat (sensible) of some level is required, and "normally" relates to requirements of the refrigeration machinery, but is calculated into the total evaporator load (vapour has poor heat transfer properties)
Did you get your managers drunk, when are you flying me over, LOL?!!!!!!!!
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I am working on it!
Been reading a few journals, apparently heat pumps are used quite alot in the lumber drying industry. Got some fairly good information on operability from a control point of view, startup/shutdown considerations (liquid in compressor, etc).
Found these guys up north
http://sylow.ife.no/hybridenergy/hybridheatpump
Seems to be a *fairly* similar type of scenario - but isn't MVR heat pump.
Will get in touch more next week so you can pick at my calculations if you have a moment!
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Drying basicallly is the the same, you need energy, it is the process that changes. so it would seem that timber and malt are same, but with malt, you do not need to worry about, about strength, twisting, warping and all the specifics required for different timber types. With the whiskey making processes each will have their own bit of magic at the different steps.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
G'day to you.
Got a couple of ancient books on heat pumps now (D.A. Reay) - very helpful.
I have now realised what would be the most efficient thing to do (i think). Use the hot water at 50C directly as the heat source. Forget about heating glycol with water.
Set a design target of achieving a glycol temperature of 70 degC. On this basis aim for a condensing temperature of 80 degC (gives a decent sized dT). 70 degC glycol will give pretty close to 60 degC air temperatures (and this is the desired starting temp, do not want higher to begin with).
Select an evaporating temperature (remove X degC from the hot water) giving a sufficent dT based on the amount of cooling which is necessary to give you sufficient Q,in + W to the glycol.
It just dawned on me that the air across the radiators will never remove a huge amount of energy from the glycol, so why bother heating with water -> then heat pump?
Glycol heated soley with heat pump to boost glycol to 70 degC would be the best thing surely. I'd expect glycol return temps to be around the 45/50 degC mark.
System would still have good control on the evaporator with hot water flow control.
Got any thoughts on this mf?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Got a couple of ancient books on heat pumps now (D.A. Reay) - very helpful.
Dave Reay is a very helpful man, indeed.
Quote:
Set a design target of achieving a glycol temperature of 70 degC. On this basis aim for a condensing temperature of 80 degC (gives a decent sized dT). 70 degC glycol will give pretty close to 60 degC air temperatures (and this is the desired starting temp, do not want higher to begin with).
Condensing temp of what refrigerant? You may want to review this aspect a little further.
You may want to look at what happens with condenser/evaporator failures if you do decide to discard secondary circuits. Perhaps I'm just reading this thread all wrong?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Condensing temperature of what indeed. Further study required on this part, alot of the old literature deals with refrigerants that may not be socially acceptable now :mad:
Looking at a P vs. Enthalpy chart of ammonia, 80degC is far from critical properties, but it's at 40bar (seems quite high, i gather 20-25 is more like what is aimed at).
I don't think you are reading wrong, but if the heat pump exchangers went tits up, the primary heating medium (steam radiators) would ramp up to cope. Would they be able to cope with heating (the now)cooler air to 60+ degC? Very good point. They might struggle without pre-heating.
However, the system can always revert back to it's old recovery (which uses the exhaust humid air to heat the glycol a wee bit). This just requires the flick of a switch / control valves (so to speak).
Any thoughts on refrigerants for this temperature range appreciated.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
The glycol loop is more than likely there for practical reasons, how cold does it get? what happens to your air heat exchanger, if there is no heat flow. (kiln is off).
Of course direct heating is better than indirect! to be determined!
Earlier on I told you that your heat pump should heat the glycol directly
As far temps go they are just pie in the sky figures, until the air heating process has been determined,
The heat pump is the very last thing to sort out.
Simply what is the temperature of the fluid entering the evap?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
I have just re read you last two statements, it could be constrewed in a number of ways.
I think you are again moving away from your whole plant process.
You have water at 50C plenty of it.
What is the required temperature of the water back at the distilling process, what happens if this colder! Does this improve the distilling process.
You already have some from of heat exchange, using your exhaust air.
Understand that the compression ratio determines the efficiency of the heat pump. Very early on I asked do you require energy or temperature, again this can only be determined by knowing the air heating process, including diversity of the kilns.
As far as refrigerant choice, what will be the working conditions, whos going to fix it, are components of the shelf, is it safe, if there is a leak will taint your product, what is the capital cost.
it is very difficult to find one that will be top in all areas.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
The process specification envelope needs to be determined before a detailed engineering phase can, or should ever, begin.
Manny - first set down your hot & cold streams, load patterns in stone, then re-visit the equipment required to get there.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Flexability is required with cold water Fridge - the temperature required can change depending on character of spirit. > 30 is too hot, 18- 28 is normal. Therefore cooling down to 30 would be ideal, but no less than 30. There is sea water cooling facilities in place to bring it to the exact requirement.
Air flow through the radiators is 24/7 - a kiln will be "off" for say 4 hours out of a 24 period, but at that time it's paired kiln will be in full whack so air flowrate is still there.
----
Trying to guess how the radiator performs at elevated temperatures is tricky, and so its really hard to know return temps that glycol would be at. I realise this is key information to know before any design can take place.
I am wondering if it is best to assume new radiators will be purchased which can be designed to best suit the new process?
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Quote:
Originally Posted by
MannyCalavera
Flexability is required with cold water Fridge - the temperature required can change depending on character of spirit. > 30 is too hot, 18- 28 is normal. Therefore cooling down to 30 would be ideal, but no less than 30 NO. There is sea water cooling facilities in place to bring it to the exact requirement.NO waste of energy (do not disconnect as may be used when ambients are very high)
Air flow through the radiators is 24/7 - a kiln will be "off" for say 4 hours out of a 24 period, but at that time it's paired kiln will be in full whack so air flowrate is still there. If your sure that the rads never drop below freezing, then water is OK direct (it can be controlled, but its risk management)
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Trying to guess how the radiator performs at elevated temperatures is tricky, and so its really hard to know return temps that glycol would be at. I realise this is key information to know before any design can take place.Correct
I am wondering if it is best to assume new radiators will be purchased which can be designed to best suit the new process?
100%
"S" is the key
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Excellent. Let's assume this is the case henceforth - no point installing a great heat pump system if the delivery of heat is going to be hindered by some old piece of sh*t radiator.
My next thought would be, what would be best glycol temperature for the condenser. Glycol returning hotter or colder? (depends on radiator design and glycol flow, both of which we can change). Colder would strike me as being better, more driving force for the condensation etc.
1.2 MW is the required duty to raise mean ambient air from 10 C to 60 C given the average air flowrate in one radiator. This is the key requirement of the glycol.
I am in contact with a fabricator of radiators up here, hopefully he can advise me on temperatures which would do this duty so i can get an idea of what temperatures of glycol to expect to achieve 60 C air-on.
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
Still moving a bit quick,
so now descibe your process (no numbers) keep it simple
I will start; we have 2 energy streams,"a' hot energy coming from the dist. process and "b"low grade heat from exhaust recovery
>
>
>
End desired results
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
- two energy streams, hot dist water and exhaust kiln air- exhaust air currently vented with no recovery- dist water currently used to heat glycol circuits- cooled dist water returned to cooling towers--------- 6 kilns in question- operate in pairs- numbered 3/4, 5/6, 7/8- 3/4 twice the capacity of 5-8- air flowrate always fairly constant- 24 kiln cycle per kiln- first 12 hours air is 100% wet, final 12hrs moisture content reduces- whilst 1 kiln is in first 12hrs, paired kiln will be in second 12hrs- this kiln will recirculate 100% air to its paired kilneach pair has 1 pre-haeting radiator- glycol passes through radiator pre-heating kiln air- cooled glycol returned to hot water PHEs- 3 pre-heating radiators = 3 glycol circuits = 3 PHEs- glycol circuit can switch between exhaust air & hot water as a heat source- hot water almost always used preferentially- exhaust air not utilised------------heat pump- use hot water as a heat source- use a heat pump to delivery energy and raise the temperature of the 3 glycol circuits- increase pre-heated air to a temp of 60 degCpro's- savings on annual HFO- CO2 considerations a positive- cooling condenser water saving on cooling costsv.s.- capital / maintenance / operating cost of heat pump
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Re: Exhaust Air to Warm water Heat Pump - malt kilning
apologies for format, copy paste didnt work :rolleyes: