R410a independent view

[mad fridgie]

Hi Boys and girls,

At present i am competing against a large company who have excellent marketing skills.
However I believe the marketing is overriding engineering priciples, not a bit, a lot to where it seems to me that the info is just out right lying!

So the machine.

It is PCM (phase change material) storage system, the PCM are in balls which are 80mm diameter and freeze at -2C
These balls are frozen by a circulating glycol (multi-pass over time). What temp would you expect the cold feed glycol to be to freeze these PCM balls?

Of course this glycol has to be chilled, after removing energy from the PCM balls, What then would you expect the SST (Te) to be?

Now they claim that the system (comp, fan and pumps) has a cooling COP of 3.3.
The system is closed coupled, the compressor is a scroll and not insulated, and is within the condenser air stream.

For ease in calculations lets say the net cooling duty is around 30kw

This is where you going to think, to achieve the COPs shown, what will the SCT (Tc) be. Knowing this what do you expect the discharge temp to be?

I am after real numbers, not pure numbers at 100% isentropic efficiency.

Thanks for those who take the challenge.

Mad.

[Rob White]

Hi Boys and girls,

At present i am competing against a large company who have excellent marketing skills.
However I believe the marketing is overriding engineering priciples, not a bit, a lot to where it seems to me that the info is just out right lying!

So the machine.

It is PCM (phase change material) storage system, the PCM are in balls which are 80mm diameter and freeze at -2C
These balls are frozen by a circulating glycol (multi-pass over time). What temp would you expect the cold feed glycol to be to freeze these PCM balls? If the balls freeze at -2 then the circulating fluid only needs
to be a few degrees below that, because the greater the Delta T on the fluid the lower the evaporating temp
will have to be.

Of course this glycol has to be chilled, after removing energy from the PCM balls, What then would you expect the SST (Te) to be? If you run the evaporating temp at about 10 Degs lower than the glycol and the
glycol a few degrees lower than the freezing point of the balls then your looking at about -10 to -15 DegC

Now they claim that the system (comp, fan and pumps) has a cooling COP of 3.3.
The system is closed coupled, the compressor is a scroll and not insulated, and is within the condenser air stream.

For ease in calculations lets say the net cooling duty is around 30kw

This is where you going to think, to achieve the COPs shown, what will the SCT (Tc) be. Knowing this what do you expect the discharge temp to be? Condensing temp will be approx 15 Deg above the ambient
air temperature. If the condensing unit was in an ambient of 25 DegC then the condensor saturation temp would
be approx 40 DegC

I am after real numbers, not pure numbers at 100% isentropic efficiency.

Thanks for those who take the challenge.

Mad.

Regards

Rob

.

[Rob White]

.

This is a screen shot with those figures, with 8K superheat and 4K subcooling.

9769

And the COP appears to be about 3.9..

Rough numbers and a lot of assumptions but
not far off what you would expect?

Regards

Rob

.

[mad fridgie]

Hi Rob,

thanks for taking the challenge.

I did not want to give all the info,

They say glycol -5C, so your evap temp would be close to -10C ( how ever i feel that both are a little warm) but will accept.

I not know of a compressor that has a isentropic efficiency of 1, more like 0.7.

The COP or EER is for a system Which includes the fan for the cond and the glycol pump. all added together equals a COP of 3.3.

[Rob White]

Hi Rob,

thanks for taking the challenge.

I did not want to give all the info,

They say glycol -5C, so your evap temp would be close to -10C ( how ever i feel that both are a little warm) but will accept.

I not know of a compressor that has a isentropic efficiency of 1, more like 0.7.

The COP or EER is for a system Which includes the fan for the cond and the glycol pump. all added together equals a COP of 3.3.

Isentropic efficiency of 1 is the default and yes you would have to put real numbers in.

The COP could be better than the EER because with COP you only calculate Refrigeration Effect
divided by the heat imparted through the compression process. With EER you are working with
total system input power and total total cooling effect so real numbers can be taken into
consideration.

But without real numbers we are only working on assumptions and you know what assumptions
make? AN ASS out of U and ME :o

Regards

Rob

.

[Gibbo]

Way back in the early 90's when ice storage was all the rage worked on some Carrier Flotronic water cooled chillers. all were recips one site was on R22 the other site was on R134A both ran at -9c leaving temperature from chiller. The theory was you used the ice storage during the day with the chiller off except during peak loads during the summer. The chiller made ice during the night on cheap tariff electricity.

Gibbo

[MikeHolm]

First thing is that the balls need to be a lot smaller than 80mm diameter. They should be closer to 5-10mm. For the phase change to work well the entire PCM should be subjected to the source temp at the same time. There are a number of solar tanks that use PCM and the performance has been really studied well. I will try and find a paper if anyone wants it.

Also, PCM can be designed to change state at different temps so......

[mad fridgie]

Isentropic efficiency of 1 is the default and yes you would have to put real numbers in.

The COP could be better than the EER because with COP you only calculate Refrigeration Effect
divided by the heat imparted through the compression process. With EER you are working with
total system input power and total total cooling effect so real numbers can be taken into
consideration.

But without real numbers we are only working on assumptions and you know what assumptions
make? AN ASS out of U and ME :o

Regards

Rob

.

I am questioning claims made by a larger company, and it comes down to 2 things.

They State, an EER 3.3 and large amonts of 75-80C hot water produced from a de-superheater. so proting the saving of each.

I have no problem that an EER of 3.3 can be achieved or large amounts of hot water at 80C, but not at the same time?

So I (we) do guess the power of the condenser fan, the glycol pump and any losses. (500w for the fan, and 1000w for the pump)

I have taken data from copeland select 7 to give me isentropic efficiency. (not 100% sure of the model, but picked the highest efficiency in the duty range)

So I need a comp COP of about 3.6 to give me an EER of 3.3.

Te (SST) I have used -10C, as have you, and 8C superheat (all useful).

So working backwards from this I got to a Tc (SCT) of 30C (which does balance as this designed to run off peak at night, say 20C ambient)

Now if I look at discharge temp (I have allowed 20% of power input as loss from the non insulated compressor, in the cond air stream) I get to a discharge temp of 62C, so the best you heat water is 62C and would have to be one hell of a heat exchanger.

[mad fridgie]

Way back in the early 90's when ice storage was all the rage worked on some Carrier Flotronic water cooled chillers. all were recips one site was on R22 the other site was on R134A both ran at -9c leaving temperature from chiller. The theory was you used the ice storage during the day with the chiller off except during peak loads during the summer. The chiller made ice during the night on cheap tariff electricity.

Gibbo

I agree I think the glycol will need to be colder than the -5C to freeze 80mm balls with a freezing point of -2C

[mad fridgie]

First thing is that the balls need to be a lot smaller than 80mm diameter. They should be closer to 5-10mm. For the phase change to work well the entire PCM should be subjected to the source temp at the same time. There are a number of solar tanks that use PCM and the performance has been really studied well. I will try and find a paper if anyone wants it.

Also, PCM can be designed to change state at different temps so......

In this situation, the design is not mine. The PCM, is fixed at -2C (a glycol/water mix i believe), compared to a Hydrated salt, more commonly used in temps above 0C.
I agree the smaller the ball, the smaller the TD required to effect change.

[Rob White]

.

The high discharge temp (to warm / heat water) is a factor I did not
allow for. If you use the superheated discharge vapour to heat water
and to de-superheat the discharge gas before it enters the condenser
you can achieve nearly 70 degC with a condensing temp at 40 degC.

At 50 degC condensing temp you could get over 80 degC but it would
only deliver about 1/2 a Kw for every Kg of refrigerant and your COP
would drop to nearer 2 than 3, so obtaining both hot water and correct
ball temp and maintain a COP of over 3 seems improbable with the numbers
I'm using.

Regards

Rob


Ps that is still working with a comp at an isentropic efficiency of 1.....
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