Nh3 Heat pumps for energy savings

[RANGER1]

Can anyone shed some light on the use, purpose of installing a heat pump system to reduce energy cost.
How does it work?

ie pre heat boilers feed water etc etc.

[Magoo]

Hi Ranger1
interesting question, the penalty with 717 is the low discharge temps.. and low gas volumes circulated per Kw.
I have done the exercise of fitting de-superheaters to existing plants for potable water and boiler feed water. Double HX's and pumps and installation costs were prohibitive. Pay back in decades. Also offered wiz bang solar htrs as well.

[RANGER1]

Could it be that other refrigerants are better to use instead of ammonia?

I have heard the suggestion of using oil coolers on screw comps is good for heat recovery, but have never seen it to date.

[PaulZ]

Hi Ranger
We are in the process of installing a Mycom heat pump system at present. This runs on NH3 and has 3 N6K comps on it.
It will be used in conjunction with gas fired water boilers.
Apparently the cost saving is considerable.
It operates basically as a condenser, suction 1000 kpa and discharge up to 3000 to 3500 kpa.
Will keep you informed as to what happens when we commission.
Paul

[RANGER1]

Hi Ranger
We are in the process of installing a Mycom heat pump system at present. This runs on NH3 and has 3 N6K comps on it.
It will be used in conjunction with gas fired water boilers.
Apparently the cost saving is considerable.
It operates basically as a condenser, suction 1000 kpa and discharge up to 3000 to 3500 kpa.
Will keep you informed as to what happens when we commission.
Paul

Thanks Paul, sounds interesting & I'II guess we will see more & more of this type of thing if it proves itself.

Australia is interesting with old machinery like screw compressors that are over 30-40 yrs old.
It makes me wonder about power savings & efficiency, as surely a new compressor has to be better, but hard to sell & prove that its saving client decent money & payback.
In the places I work heat recovry is not worth the capitol outlay. I guess a new factory or process has to be built with all these new ideas to save on power, with heat recovery etc

[mad fridgie]

This can be complex, but firstly as you have indicated, you do need to complete an energy to fiscal analysis.
I produce high temp heat pumps producing water at 85C plus and eCOPs of upto 9 at these temps, with energy savings that can exceed over 200% of the water heating bills. So it can be viable to install these type of machines. I have not designed NH3 system for this application, but I see little reason why not.
Most big plants, either do not use enough hot water (pure cold storage) or they already have low cost water heating, or require steam which is potentially doable with a heat pump, but i do say this with a bit of caution.

[sterl]

Very large circuits for "campus heating" or whole-town hot water heating going into Norway and other places.....Tip of the iceberg, literally but see:

http://www.emersonclimate.com/Docume...%20%282%29.pdf

Applying condenser heat for alternate uses on a conventional Big Industrial circuit does have some opportunities mostly for climate control but the easier way to get some medium high temperatures for hot water and the like is to utilize the oil coolers....Pretty compact heat exchanger on a 500 Hp compressor will make 12 GPM of boiler water rise from 60 to 140 deg F and the heat available remains just about the same irrespective of the actual load on the machine.

[Magoo]

Hi ranger1.
as per PaulZ post, 10 Bar/g suction and 35 bar/g discharge I beleive would be outside the critical and stable conditions for R717, I could be missing something here, but will look at it.

[mad fridgie]

Hi ranger1.
as per PaulZ post, 10 Bar/g suction and 35 bar/g discharge I beleive would be outside the critical and stable conditions for R717, I could be missing something here, but will look at it.

NO well within the "bell" 110bar plus, for critical

[CoolDay]

The industrial refrigeration community has regularly utilized heat recovery strategies to tap into the 10% to 15% of high grade sensible heat available with desuperheaters and from oil coolers. But there's a significant difference between heat recovery and heat pumps.

Heat pumps raise the condensing pressure to a level corresponding to the desired temperature of a heated medium such as water, allowing the FULL use of the total heat of rejection for beneficial heating purposes. In food and beverage processing, such heat can be used in place of fossil fuels to heat water up to 130F, or 165F, or higher, for sanitation, scalding, blanching, pasteurizing, bottle washing/warming, boiler preheating, water heated by steam injection, etc. Outside of food processing the opportunities are endless.

For nearly 150 years we, as an engineering community, have acknowledged that it’s acceptable to reject to atmosphere all of the valuable heat absorbed through ammonia refrigeration processes, plus the added heat energy of compression, while simultaneously consuming massive amounts of fossil fuels (at a COP never greater than 1.0!) to satisfy simultaneous heat loads. WHY? The IEA Heat Pump Centre claims it’s due to compressor limitations.

There are well recognized limitations of traditional ammonia compressor technologies—limitations in their ability to operate at the higher pressures and temperatures required for heat pumps. Consider reciprocating compressors and the internal forces on their cranks, rods, pins, and bearings, as well as the chattering of valves and springs. Since reciprocating compressors are not ‘oil-flooded’ like screw compressors, their discharge temperatures are considerably high (+200F) and not as manageable as with screw compressors. The inherent reciprocating action leads to regular service intervals and parts replacement even in the low pressure/temperature operation of conventional refrigeration duty. Now consider the effects on a recip compressor of operating at the much higher pressures and temperatures required for heat pump duty. The service intervals at these conditions are considerably shorter, and oil degradation is accelerated.

Consider the other traditional ammonia compressor technology: twin rotor screw compressors. In regard to temperature, twin screws are better suited to operating at higher condensing conditions since discharge temperatures can be managed with oil cooling. Yet in regard to pressure, the twin screw is subject to significant limitations...axial and radial thrust loads impart higher loads on the bearings, accelerating their wear; increased pressure leads to rotor deflection, which in turn leads to a loss in volumetric efficiency and potential wearing of the rotors against the casing and slides; minimum inherent volume ratios inhibit their ability to optimize performance, resulting in over-compression and further compounding the bearing load and rotor deflection limitations.

In observing the operation of single rotor screws in high pressure (400 to 800 psia) natural gas applications, an ex-Sabroe compressor engineer readily recognized the technology as “what the world’s been waiting for” in an industrial heat pump compressor. With the first of 14 installations now operating for more than 2 years at a major food processor’s chocolate confection plant, it’s becoming widely accepted that single screw compressors are unique in their ability to operate in industrial ammonia heat pump applications.

[PaulZ]

Hi All
The Mycom heat pump has been commissioned and is operating well. The suction can run to 1200 kpa and this is what we have set as discharge pressure on the plant when the heat pump is operating. The discharge on the heat pump operates at about 4500kpa when we have enough discharge to satisfy the heat pump, if the load is light the discharge can drop to about 3500kpa.
Only 2 compressors operate at one time. The system condenses about 2 ton of ammonia / hour when running at full capacity and will heat incoming water from 17oC to about 60oC at a flow of 3.6 l/s. We are supposed to be able to get the heat pump hot water tank to about 70 / 75oC when recirculating, normal continuous use is about 58oC water to the boiler storage tank.
Don't know what sort of gas savings the client is going to make.
Paul

[mad fridgie]

Hi All
The Mycom heat pump has been commissioned and is operating well. The suction can run to 1200 kpa and this is what we have set as discharge pressure on the plant when the heat pump is operating. The discharge on the heat pump operates at about 4500kpa when we have enough discharge to satisfy the heat pump, if the load is light the discharge can drop to about 3500kpa.
Only 2 compressors operate at one time. The system condenses about 2 ton of ammonia / hour when running at full capacity and will heat incoming water from 17oC to about 60oC at a flow of 3.6 l/s. We are supposed to be able to get the heat pump hot water tank to about 70 / 75oC when recirculating, normal continuous use is about 58oC water to the boiler storage tank.
Don't know what sort of gas savings the client is going to make.
Paul

Heating COP of about 4

[RANGER1]

Thanks Paul for the update.
Mayekawa are also using a CO2 heat pump which they are promoting at the moment in Melbourne.

I know there will be more applications for this type of energy savings but see Europe, USA have more
of a use for heat pumps etc due to their obvious different climate & need for heating.

[PaulZ]

Hi Ranger
They have installed 3 CO2 heat pumps in Darwin these are used for domestic hot water.
I reckon they will have something on heat pumps at ARBS next week.
Paul

[RANGER1]

Hi Ranger
They have installed 3 CO2 heat pumps in Darwin these are used for domestic hot water.
I reckon they will have something on heat pumps at ARBS next week.
Paul

Paul they quote 65-90 deg C water 1000 l/hr so resonably significant capcity.
Although if we had that much hot water at home I'm sure my wife would use it!

[piewie]

Hello PaulZ

What are you using the suction for?

[piewie]

Hello Ranger
The plant I ran in the UK, originally had the air-conditioning for the office block run off the -10 ammonia plant. It never quite worked as was intended so in an effort to correct this and to get it working properly I did major changes. Originally the contractor installed a PHE which in summer took liquid from the -10 plant and produced cold water which was bulked in a 2250l insulated tank and then pumped to the building and returned via the PHE to the tank. Then in winter with a valve changeover it took hot discharge gas and attempted to utilise the PHE as a de-super-heater. There were a few flaws in the process though. Due to the resistance across the PHE one had to partially close a regulating valve in the normal discharge line to force the hot gas through the PHE. This naturally forced the discharge pressure up and the energy consumption of the compressors naturally increased. So any cost/energy savings were lost. The system was also terribly un-reliable as due to the fluctuating load on the compressor low side the heat recovery was not consistent. The heat losses in the building however are fairly constant in winter so the water temp would peak and trough constantly and the complaints were never ending.
Cost in this case was not a real issue, as to replace all the A/C units in the building would have cost a fair bit. We changed the system and added a de-super-heater which we purpose built and plumbed into the system. I also changed the water into a mild glycol mixture. I changed the water pipework a bit and utilised the standby pump as a recirculating pump in winter. This pumped the glycol mix through the de-super-heater and back to the tank. The other pump pumped the glycol mix to the A/C units. To aid in temperature control I fitted a VSD to the recirculating pump and with a little bit of PLC programming I arranged a simple PI analog to digital loop which changed the speed of the pump to keep the glycol temp constant. This I set at 50 celcius it worked great and was never more than a degree out of spec. Then in Summer a flick of a switch (SCADA) and two glycol valve chages and the system would produce zero degree water. The whole system is still working today.
In 2009 I was instrumental in the design and construction of a new section (48000 cubic meters)of frozen (-25) store. Frost heave is a serious problem in the UK. So it was decided that it was imperative to move away from the norm of electric under floor heating. Partly due to energy costs and hugely due to the un-reliability and maintenance issues. So here we made use of the oil cooling on the 3 x SAB85/87 screw compressors. This was free energy. The cost of running the system is merely the cost of the little 1kw pump. Even this pump seldom runs at 50Hz. The biggest cost was the installation and the payback period is not very long. But the savings in terms carbon are there. The cost in terms of maintenance is still zero. The biggest headache on this work was getting the stupid builder to understand exactly how to install the pipes.
These sort of projects are the ones that really count as we are making use of as much of the energy as possible and every little bit counts. Energy costs are really heavy in the UK and Australian energy only costs about a third (pre-Juliar Carbon Tax) so the payback periods are shorter. But I think this might all change at $20/tonne.
I am still not a great fan off heatpumps though as even though they might have better eCOP figures than conventional heat sources there is still a great deal of energy wasted.

[PaulZ]

Hi piewie
The suction I am referring to is the ammonia plant discharge gas.
Paul

[piewie]

Can you please draw me a picture. I am truly lost here.

Regards Piewie

[mad fridgie]

Hi piewie
The suction I am referring to is the ammonia plant discharge gas.
Paul

Is this just multi-stage or a semi- cascade system (each refrigeration loop is totally separate)

[PaulZ]

Hi Mad
The heat pump is single stage, we are running 2 compressors when the load is available and have one as standby. The main plant is 2 stage, one low stage screw one high stage screw running 3 plate freezers, freezer store, chiller store, load out and a couple of other chill rooms.
Paul

[mad fridgie]

Hi Mad
The heat pump is single stage, we are running 2 compressors when the load is available and have one as standby. The main plant is 2 stage, one low stage screw one high stage screw running 3 plate freezers, freezer store, chiller store, load out and a couple of other chill rooms.
Paul

Hi Paul,
So the heat pump refrigerant circuit is totally seperate to the main plant circuit.
So you have the discharge of the main plant going into one side of the heat exchanger and the evap side of the heat pump on the other side of the heat exchanger?

[PaulZ]

Hi Mad
There seems to be a bit of confusion here. This Heat Pump is basically another condenser on the main plant.
The discharge of the main plant is the suction of the Heat Pump plant and the condensed liquid goes back to the receiver. The water is first heated in a subcooler which full of condensed liquid then the water goes through the condenser and is heated further. Both the the subcooler and the condenser are Shell and Plate heat exchangers.
Paul

[mad fridgie]

Hi Mad
There seems to be a bit of confusion here. This Heat Pump is basically another condenser on the main plant.
The discharge of the main plant is the suction of the Heat Pump plant and the condensed liquid goes back to the receiver. The water is first heated in a subcooler which full of condensed liquid then the water goes through the condenser and is heated further. Both the the subcooler and the condenser are Shell and Plate heat exchangers.
Paul

Thanks paul,

That is the way I would of thought it was done. A third stage added to the main system.