AKV versus TEV

[Peter_1]

Need some good advice:
Had a meeting yesterday with an engineering office (EO).
They had prescribed AKV's where I had suggested TEV's.

Their argument was that they could lower the energy bill with at least 15%. That sounded music in the ears of the owner but for me it seemed figures Danfoss themselves gave them.

He said that decreasing one 1°C in condensing pressure can lower the energy bill with 2%. Correct you think?

The argument was that they with the AKV's can lower the condensing pressure significantly and rise suction pressure, without loosing a good liquid injection in the evaporator.

I stated that the biggest advantage should be lowering the condensing pressure but that this can also be done with conventional TEV's if you had selected them to this 'special' working conditions (= low condensing pressure)

He said that my condensing pressure should follow the outside temperature (which is of course correct) but that the injection of the AKV's is constantly adapted to the outside temperature.
What he tried to explain - I think - is when the HP decreases due to lower ambient temperatures, the injection pulse should also been longer to remain at the same SH setting.

I argued that if the condensing pressure goes up and down with TEV's, then the sensing element of my TEV will send a signal - in this case a mechanical or pressure signal and not electronic - to my TEV so that a constant superheat will be maintained if Hp decreases whereby TEV injects not enough liquid. Same - perhaps a little bit higher - as with AKV's.

He said that we then needed to go on site (with TEV's) several times a year, each time the outside temperatures should change to adapt the superheat settings of all our TEV's.
I completely disagreed whit that.

If you look in the manuals of Danfoss (haven't them here not with me), then you can see that TEV's still keeps function properly even with low DP's over it. (but with a lower capacity at lower DP's of course)

My point was - but I can be wrong - that the higher price of AKV's, compared to TEV's will never be repaid by a lower energy bill.
We are talking about a small meat factory with 10 evaporators in the range from 2 kW till 7 kW, total capacity 45 kW.

We also proposed a heat reclaim for water (+/- 1.000 l and additional lowering of condensing pressure) but now they doubt that the costs for this will ever be repaid.
We even proposed a ground coil below the inclined loading docks (we did this already twice) to de-ice them and make so also an additional condenser.

That should have lowered the energy bill.

So, I need some feedback from you guys.
Where am I wrong, where am I right, what different opinions you have, what arguments can be given to justify my idea's? Numbers, tests, testimonials, calculations... anything is welcome because we want this case.

Just found this pdf http://mfnl.xjtu.edu.cn/edu-dk-et/St...ion_system.pdf

I doubt if this is a 100% neutral test. It's done in Denmark with Danfoss material, Danish professors,measured with Danfoss material...

[Andy]

Peter
during discussions with one of my competitors, we discussed the merits of akv's. On large supermarkets there is an advantage, you could select your tev's on a low dp, but they would/maybe be inclinded to hunt at higher ambients. For a small job such as this I think the cost will out weigh the benifits. Larger cooler still require the same valve+controller, making the cost more attractive. On the other hand there maybe some grants available to ofsett the cost.
Better fit convensional tev's, with liquid pressure amplification, boosting the lost in dp due to low condensing by use on a small pump on the liquid line.
Kind Regards. Andy.

[Budokan]

Peter,

In my opinion I would agree with the engineering office, the AKV valves would perform better the a mechanical TEV.


Without knowing all the facts it would appear that they are looking for a low energy system via a low condensing pressure. At the moment I cannot find the relevant info but although the Danfoss catalogue supplies performance data for DP as low as 2 bar I am sure they they require at least a 6 bar DP to operate. The only viable option for a low condensing presure system would be a AKV or a balanced port TEV. The only concern with a balanced port TEV ties in with the point raised by the engineering office that if the valve was selected for a low DP in high DP conditions the valve could have poor control, possibly requiring seasonal superheat adjustment.

If the main concern is the extra cost for the AKV valves/controls if you selcted the correct controls package i.e. not Danfoss you may find that the AKV valves are a viable option.

[Peter_1]

Peter,

...it would appear that they are looking for a low energy system via a low condensing pressure. ....supplies performance data for DP as low as 2 bar ....

Isn't realistic: at -10°C evaporating will say condensing at 3°C. How is this possible without a compound compressor?
Let's face it, a DP of 5 is an absolute minimum in a common supermarket.

The only viable option for a low condensing pressure system would be a AKV or a balanced port TEV. The only concern with a balanced port TEV ties in with the point raised by the engineering office that if the valve was selected for a low DP in high DP conditions the valve could have poor control, possibly requiring seasonal superheat adjustment.

Let's say we will evaporate at -10°C or 3,4 bar (50 psi) and we take a mean outside temperature of 10°C (mostly during the day 15 and 30°C in summer) but I'm not optimistic, this means condensing at 20°C or 10 bar (150 psi) for 10 K. This is a DP of 7 bar.

Let's take a TEX2 - orifice 3, for a needed capacity of 6 kW. A 4 should be too big, therefore we should work on a DP of 2. A 3 needs 6 DP.

The previous 7 bar DP gives us 6,2 kW. Suppose it becomes colder, let's say freezing, condensing at 10°C -->4 DP gives 5,1 kW and it becomes warmer let's say 30°C or condensing at 17 bar gives a DP of +/-13 so 7,2 kW. Valve will perhaps hunt a little bit (but that's what an AKV is also doing but with a smaller frequency) As far as I can remember, hunting is dangerous to damage the compressor but when it hunts, you're sure that the evaporator is sometimes overfilled with a change of insufficient superheat.
IF it will hunt.

If the main concern is the extra cost for the AKV valves/controls if you selected the correct controls package i.e. not Danfoss you may find that the AKV valves are a viable option.

Main concern is not the cost, on the contrary. If I can sell them like asked by the engineering office, I earn more.

But 1st, the client is someone who did already a lot for me, believed in me when I started in the refr business long time ago, and still believes in me and I don't want that he pays for something which will - in my opinion - never pay back the investment. I'm thinking by myself: 'If it should be for me, should I do this?'

2nd i hate it to install things in which I don't believe 100%. I don't say that AKV's are not a good product but they have to be used in the right applications. If someone can convince me with good arguments, then I go for it. But till know, I haven't got any.

And besides that, I believe more in the stepper controller EV then in PWM ones. We had a thread around this some time ago but there were almost no replies.

[Budokan]

Peter,

Most low energy systems are sold on the idea that when the climate allows they can operate with condensing temperatures that track the ambient. In your example you use an example of a system with a 7 bar DP which would still have enough design capacity if the DP dropped to 4 bar. This sounds fine in theory however how well would the pack run in these conditions because the TEV's would struggle to operate as required.

One point that would be useful to clarify is what is the required minimum supplied liquid pressure required for a TEV to operate correctly.

[Peter_1]

Peter,
In your example you use an example of a system with a 7 bar DP which would still have enough design capacity if the DP dropped to 4 bar. This sounds fine in theory however how well would the pack run in these conditions because the TEV's would struggle to operate as required.

Why should the pack run worser due to this? See lower

One point that would be useful to clarify is what is the required minimum supplied liquid pressure required for a TEV to operate correctly.

2DP (!!) according to Danfoss manual.

Just thinking on the following: what if we subcool the liquid mechanically?

But I believe in the technique of Hy-Save (See Marc has joined) together with TEV's, more then I believe in the AKV's.
In fact, with an AKV, you even can't use a Hy-Save or it's almost useless. Is this correct?

[Kevin Yeo]

Dear Marc,

In Malaysia climate, ambient temp is ard 35 deg C. Typical cond pressure is 220 psig [42-45 deg C approx]. Condenser capacity is based on net cooling capacity + heat from compressor, rated at 45 deg C condensing temperature. Delta T of 10 deg C for condenser heat transfer.

As I am really a novice for Hysave system, all i can notice from Pressure Enthalpy chart is reduced compression ratio [energy saving, less work for comp] so in another words, reduced discharged & condensing temperature. Is there any change when it comes to condenser selection.? As I know, it needs to maintain a certain Delta T for heat rejection to ambient, right? Thanks for your enlightenment.

[wambat]

THIS WAS POSTED MAY 2001

Baltimore, MD


Danfoss has conducted a controlled test in a Buffalo, NY, store using Danfoss Smart Case Controller’s and our AKV10 electronic expansion valves (EEVs).

The test consisted of one two-stage and one medium-temperature rack operating 48 evaporators. A contractor field-installed EEVs in parallel with factory-installed thermostatic expan-sion valves. Solenoid valves were also installed to allow switching between the electronic and thermostatic valves.

The valves were alternated every second day to neutralize day-to-day load variations due to shopping, stocking, and cleaning activities. Test data were recorded for four months.

The average daily usage was found to be 703 KWh on thermostatic days and 639.4 on days when the EEVs and Smart Case Controllers were used, for a savings of 9.05%. Savings increased steadily as the weather warmed, from 7.5% in March to 9.9% in June.

Savings from 4.3 to 50.8% were realized from reduced compressor run time, reduced defrost duration, and improved recovery. Average defrost was quicker by 28.7% on one rack and 17.4% on the other. Also, the test revealed higher average suction pres-sures for all three suction groups tested.

It should be noted that the savings generated from EEVs are the result not of the valves, but from the software algorithms within the Smart Case Controllers. Algorithms also determine the stability of the fixture temperatures achieved. Both of these facts were proven by the test results. The entire test’s data collection and test report were audited by the public utility serving the store. Based on the results, a rebate program was established.

[SNi]

Hi

In case of AKV you should be very carefull with the liquid velocity. It must be around 0.6 - 0.8 m./sec. (not more) otherwise AKV can be broken (liquid hammering). Price for the tube in this case will be expensive. But You can adjust MOP which You need, sometimes it`s very important.
Energy in Russia costs almost nothing, but price for AKV + controller is high enough and in this case i try to offer CAREL E2V instead of DANFOSS.

[homelover]

Hi all,
I look at it this way,
The worst thing about electronic valves are the probes that control them, they are usually cheap and fail often, especially the evaporator probe due to ingress of moisture or ice damage, If you lose the evap probe the unit will fail due to the lack of superheat, If you lose the suction probe due to the wide superheat you can flood the pack or compressor with liquid,

The benefit of electronic is only 1 valve ie no solenoid needed,

As for saving energy It sounds good but i'm one for the tradition valve that will work without probes or elctronics.
As I work daily with Electronics and Akvs, most of the problems are with probes failures, There are decent probes out there but due to the high cost no one will buy them.
Stick to the conventional valves,
And you won't spend your days changing probes.

[Latte]

Hi Guys,

I've got to aggree with homelover, TEV's are just far less hastle.

Most engineers keeps Danfoss TEV's and orrifices on their van, how many people keep AKV10 spares. Also you are not relying on two probes to control it, just one cowboy not putting probe 3 or 4 in the wrong place or loose on the pipes and off it goes.
I do tend to aggree with Danfoss that an AKV is probably cheaper to run, BUT they are only taking into account power usage and not taking into account money spent on call outs when probes fail or downtime going to get AKV spares

YES, i am old and like things the old way but when it comes to TEV's - if it ain't broke don't fix it

Regards

Fatboy

[Calvin Becker]

Good work Marc. Long time buddy!