Exhaust Air to Warm water Heat Pump - malt kilning

[mad fridgie]

Ok I will re-look through and see what else I can come up with based on what you're saying fridgie. Not much mental capacity today, birthday yesterday and whisky does not sit well ontop of alot of red wine apparently.

Will get in touch later in week.

Cheers, Manny

There is a saying never mix grape and grain.
heres another clue, in a perfect world we would use the condensor of the heat pump to directly heat the air, this would give maximum efficiency (this is not a ruled out option, but info indicates that this would be an unlikely option, for practical, technical control reasons), so what would be the next best method?

[MannyCalavera]

Direct condenser use to heat the air had crossed my mind Mad, however if the refrigerant vapour is super-heated, is it not the case that poor heat transfer coefficients between air / vapour would cause an issue?

I am not sure how superheated the vapour would be, if it was a large amount or just sitting above condensing temperature.

I presume you are indicating towards direct glycol-refrigerant heat exchange.

From that viewpoint I can see a couple of methods; 1) Use the hot water as a source, and use refrigerant on the glycol loop to heat it.

2) Keep the hot water-to-glycol PHE as it is, and then use the warm water as the heat source of the heat pump, and use this high temperature refrigerant to further heat the glycol

Tomorrow i will sit down and think more about why this is more / less advantages & efficient.

Cheers.

[mad fridgie]

Direct condenser use to heat the air had crossed my mind Mad, however if the refrigerant vapour is super-heated, is it not the case that poor heat transfer coefficients between air / vapour would cause an issue?
No this not the issue with the direct system, it more to do with the amount of refrigerant and where it sits (hard to explain in a few words)
I am not sure how superheated the vapour would be, if it was a large amount or just sitting above condensing temperature.
The process determines the superheat temp and the amount of usable energy, remember one of the first questions do you want temp or energy.

I presume you are indicating towards direct glycol-refrigerant heat exchange.
Correct

From that viewpoint I can see a couple of methods; 1) Use the hot water as a source, and use refrigerant on the glycol loop to heat it.

2) Keep the hot water-to-glycol PHE as it is, and then use the warm water as the heat source of the heat pump, and use this high temperature refrigerant to further heat the glycol.
Correct, now you are getting it, but do not at this stage discount the other options, as you need to look at yearly load profiles and how changes in the air temp effect the process loops

Tomorrow i will sit down and think more about why this is more / less advantages & efficient.
Also remember that we have power limitations, (1 MW) so it now about best use of energy not temperature.

Cheers.

Keep up the good work

[MannyCalavera]

"Correct, now you are getting it, but do not at this stage discount the other options, as you need to look at yearly load profiles and how changes in the air temp effect the process loops"

yes good point sir, I guess i need to come up with a couple of spreadsheets for the different setups, with all the yearly process condition changes and assess how each one would respond and have a punt at how effective it would be.

Hope the UK weather is treating you well, very nice up north!

[MannyCalavera]

Got a fair document of all the process variables now, in terms of flow and temperatures and operating times. There is physically room also on site around the HX / hot water recovery shed.

I bet you won't like this question; where should i start when thinking about compression?

Need to compress refrigerant to a pressure such that it will condense T,c above T,sink. That's all i know.

Compressor type (screw?), ideal compression ratio's, superheat temps achieved - any guidance on this area of design?

Perrys Chemical Engineer handbook has the theory but again I sense it will be unpractical

Any input appreciated.
NB i am still thinking about the process first and pump second, fear not.

Cheers,
Manny

[mad fridgie]

Got a fair document of all the process variables now, in terms of flow and temperatures and operating times. There is physically room also on site around the HX / hot water recovery shed.

I bet you won't like this question; where should i start when thinking about compression?

Need to compress refrigerant to a pressure such that it will condense T,c above T,sink. That's all i know.

Compressor type (screw?), ideal compression ratio's, superheat temps achieved - any guidance on this area of design?

Perrys Chemical Engineer handbook has the theory but again I sense it will be unpractical

Any input appreciated.
NB i am still thinking about the process first and pump second, fear not.

Cheers,
Manny

You are right, do not like the question,
The question can not be answered, unless you know all process variables.
This will determine the type of compressor, also possible refrigerant choice, all these effect SST, SCT, superheat, sub cooling thermal amd mechanical loss. Which all change as the processes change.
Not much help at all, sorry!!!

[MannyCalavera]

No worries Fridgie, saw that coming. If i were to submit a reply / word doc with a detailed breakdown of all the process variables with the degree of variation depending on process / seasonal changes / other factors, along with numerical values that i have given before (but now refined), and a detailed physical layout, would you be able to (with your experience in the industry) look at that and go

"so this is changing, this is constant, you have this much energy available, this is what you require, blah blah" and from that be able to describe a setup which would be suitable?

I have worked through this data the last two weeks and will compile it for next week, upload it here also for perusal. It will list all variables which effect the glycol system / magnitudes of flow and all foreseeable variation, seasonal or otherwise.

It would be easier if you could transfer information like in The Matrix, so I wouldn't need to keep asking questions here

"Want some more?"
"Hell yes."

[mad fridgie]

No worries Fridgie, saw that coming. If i were to submit a reply / word doc with a detailed breakdown of all the process variables with the degree of variation depending on process / seasonal changes / other factors, along with numerical values that i have given before (but now refined), and a detailed physical layout, would you be able to (with your experience in the industry) look at that and go

"so this is changing, this is constant, you have this much energy available, this is what you require, blah blah" and from that be able to describe a setup which would be suitable?

I have worked through this data the last two weeks and will compile it for next week, upload it here also for perusal. It will list all variables which effect the glycol system / magnitudes of flow and all foreseeable variation, seasonal or otherwise.

It would be easier if you could transfer information like in The Matrix, so I wouldn't need to keep asking questions here

"Want some more?"
"Hell yes."

The simple answer is "yes"
I suspect that you are still a lttle away from this stage, but i will have a quick look, but you are now moving into info that is in the commercial field "well you have been it it for quite some time"
By now you should have come up with some very basic savings and a rough acceptable return on investment (not the same as the equipment cost, but a limit to the cost, give or take), so I do not see me giving you the design method, but a results method, prop. not what you would ideally want.
cheers
Mad

[MannyCalavera]

Doing some cost evaluation.

Mad I recall you used a figure of ~ £400k + for the cost of heat pump plant. Is this realistic?

I presume capital cost doesn't really increase with heat pump load, this would just be an operating cost?

For the sake of doing some evaluation is it possible based on the type of system I have described to give a rough power requirement for compression? 200-300kW, for example?

Any punts welcome, or other related capital / operating costs to take into account.

Cheers

[mad fridgie]

Doing some cost evaluation.

Mad I recall you used a figure of ~ £400k + for the cost of heat pump plant. Is this realistic?

I presume capital cost doesn't really increase with heat pump load, this would just be an operating cost?

For the sake of doing some evaluation is it possible based on the type of system I have described to give a rough power requirement for compression? 200-300kW, for example?

Any punts welcome, or other related capital / operating costs to take into account.

Cheers

Capital cost really does change with heat pump load.
If you are looking at 300kw power draw, then you should be well in with 400,000 pound.
At this stage you could calculate on a COP of 4 (1200Kw), this would give you an approx saving of 24 pound an hour
cheers
Mad

[MannyCalavera]

Done some quick cost work;

Electricty per kWh = £0.08

Based on mass&energy balance, gaining +1degC air preheating all the 3 paired loops (6kilns) saves £38,000 annually

Say power consumption of heat pump was 200kW
8000hr working year; £125,000 annually on elec.

Being optimistic and assuming a COP of 6,

200kW in = 1.2MW out

Average hot water flow to be assumed ~ 200m3/hr

Temperature lift due to 1.2MW ~ 5.2 degC

Savings on fuel oil ~ £205,000

Annual saving; £76,000

Very rough and ready calcs but a fair saving annually.
Any comments?

Cheers

[mad fridgie]

have you an updated cost of the fuel heating i thought t was 4 pence Kwhr

[MannyCalavera]

11.7 kWh/litre

~ £0.47 per litre

£38,000 comes from air mass flowrate across the 6 kilns

each batch ~ 90,000kg air per hour

4 batches at any one time

[mad fridgie]

11.7 kWh/litre

~ £0.47 per litre

£38,000 comes from air mass flowrate across the 6 kilns

each batch ~ 90,000kg air per hour

4 batches at any one time

0.47 / 11.7 = 0.04pound/kwhr

So 1.2mega watt saving *8000 hours * ).04 =
Yeary saving on fuel 384000 pounds,
less electric running cost
125000 pounds,
actual saving 250,000 pond

[MannyCalavera]

With you on elec Fridgie, substantially higher fuel savings than i am getting.

May I ask your assumed/calculated CoP?

At this stage I am to present initial findings to some people in the company.

I feel i have got a good enough understanding of design considerations to present the case to them for use of a heatpump. Work will be ongoing until xmas and i'm sure by then i can present a more detailed case of the proposed setup(s).

Thanks for all the guidance up till now Mad, very much appreciated. Any developments, i will post here.

Regards

[mad fridgie]

With you on elec Fridgie, substantially higher fuel savings than i am getting.

May I ask your assumed/calculated CoP?

At this stage I am to present initial findings to some people in the company.

I feel i have got a good enough understanding of design considerations to present the case to them for use of a heatpump. Work will be ongoing until xmas and i'm sure by then i can present a more detailed case of the proposed setup(s).

Thanks for all the guidance up till now Mad, very much appreciated. Any developments, i will post here.

Regards

Calcs have to been made using same data,
you stated 8000 hrs run time, at 200Kw and COP of 6 (I have no idea where this figure came from) so you must also calculate the fuel savings based upon the same run hours. 1.2Mw * 8000hrs. To be conservative
I would use your 8000 hr run time (seem reasonable)
I would how ever use a COP of 4 or 300Kw power draw to produce 1200Kw of heat energy, the you can convert to an annual pound value.
cheers
Mad

[MannyCalavera]

Been reading an online pdf "Industrial heat pumps for steam and fuel savings". It outlines a method to estimate COPs and savings for a system for mechanical heat pumps.

Basically you estimate your heat pump inlet temperature (function of heat source temp) and the heat pump outlet temperature (you can set this, but need to factor in sufficient approach temp for the condenser).

CoP is then estimated as T,out / (T,out - T,in)
, in degrees Rankine.

Take an efficiency of 70% from ideal CoP, and this gives you an approximate CoP based on the temperatures you have specified.

I have done this and get 6.1.

Then Work,in = Q,in / (COP - 1)

which turns out to be 180kW (compressor power i presume).

Q,out = Q,in + Work,in


From this method it seems that the inlet and outlet temperatures of the heat pump (compressor) play a large role in efficiency. Is this fairly true?

I see what you mean about needing all the process variables tied down, playing around on Excel, even small changes in flow / temp massivly change efficiencies.

Cheers

[mad fridgie]

Been reading an online pdf "Industrial heat pumps for steam and fuel savings". It outlines a method to estimate COPs and savings for a system for mechanical heat pumps.

Basically you estimate your heat pump inlet temperature (function of heat source temp) and the heat pump outlet temperature (you can set this, but need to factor in sufficient approach temp for the condenser).

CoP is then estimated as T,out / (T,out - T,in)
, in degrees Rankine.

Take an efficiency of 70% from ideal CoP, and this gives you an approximate CoP based on the temperatures you have specified.

I have done this and get 6.1.

Then Work,in = Q,in / (COP - 1)

which turns out to be 180kW (compressor power i presume).

Q,out = Q,in + Work,in


From this method it seems that the inlet and outlet temperatures of the heat pump (compressor) play a large role in efficiency. Is this fairly true?

I see what you mean about needing all the process variables tied down, playing around on Excel, even small changes in flow / temp massivly change efficiencies.

Cheers

You can have what ever COP you want, comes down to what numbers you put "in", add what does this come down to, you have guessed it "The Process"
Refrigeration is all about compression ratios.
So here is a question to keep you thinking and is topical
Is better to produce 1MW of heat with a COP of 6 or produce 4MW with a poor COP of 4
(Back in NZ)

[MannyCalavera]

4MW with a COP of 4 would have larger savings. I see your point there.

I have come to realise that conditions won't vary as much in winter as i had presumed. Cold air over the glycol radiators won't remove a much larger amount of energy from the glycol. Delta T across glycol likely to change only slightly.

Anyway I have a question. Being in the heat pump business you must keep a close eye on the relative cost of electricity versus fuel oil.

And of course this has a large influence on heat pump economics and profit. I know you are in NZ but have some UK knowledge - over the next 2, 5, 10 years - do you reckon this will swing in favour of elec:fuel oil? Or will the CO2 aspect be the larger driver?

[mad fridgie]

4MW with a COP of 4 would have larger savings. I see your point there.

I have come to realise that conditions won't vary as much in winter as i had presumed. Cold air over the glycol radiators won't remove a much larger amount of energy from the glycol. Delta T across glycol likely to change only slightly. Correct, work is need on this area, (large savings can be made here)

Anyway I have a question. Being in the heat pump business you must keep a close eye on the relative cost of electricity versus fuel oil.

And of course this has a large influence on heat pump economics and profit. I know you are in NZ but have some UK knowledge - over the next 2, 5, 10 years - do you reckon this will swing in favour of elec:fuel oil? Or will the CO2 aspect be the larger driver?

This is only an opinion, I suspect that the difference between the price of a raw heating fuel (any) and the price of electricity will become somewhat closer, as focus is given on renewables (wind, wave, solar and I also think nuclear will rise again) The CO2, well your guess is as good as mine, I think we should look at protecting resources, more than focusing on a reason for protecting them.

[MannyCalavera]

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.

[mad fridgie]

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

[MannyCalavera]

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.

[mad fridgie]

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.

[MannyCalavera]

Just to confrirm Mad, when you talk about "load profiles" - this is the expected duties/range of variation on the condenser and evaporator?

[mad fridgie]

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

[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?

[r.bartlett]

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' ?

[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.

[r.bartlett]

^ 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.

[MannyCalavera]

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

[desA]

This thread is an interesting read. Keep it up everyone.

[MannyCalavera]

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.

[mad fridgie]

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

[mad fridgie]

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.

[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.

[mad fridgie]

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.

[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.

[mad fridgie]

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.

[mad fridgie]

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.

If you want the best, you pay for the best

[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

[mad fridgie]

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

[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?

[mad fridgie]

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!

[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 ?

[mad fridgie]

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 ?

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?!!!!!!!!

[MannyCalavera]

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!

[mad fridgie]

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.

[MannyCalavera]

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?

[desA]

Got a couple of ancient books on heat pumps now (D.A. Reay) - very helpful.

Dave Reay is a very helpful man, indeed.

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?