TechNet-21 - Forum

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  1. Dave Klassen
  2. Cold chain equipment
  3. Friday, 21 December 2018


I am brand new to TechNet-21 so this will be my first posting. 

I am trying to find an SDD (Solar Direct Drive) freezer which will maintain -10C and below. The product I need to store in Nigeria is surfactant (injected into the lungs of premature babies with collapsed lungs to give them life) which must be kept at that cold temperature to maintain a shelf life of 3 years. The electricity supply throughout the country in Nigeria is erratic and undependable, thus I would like to install an SDD freezer with a distributer (in Lagos) which would be independent of grid power. Surfactant is a very high value and low volume product so a smaller (50-100 liters) SDD freezer would be ideal.

My understanding is the freezers designed for freezing ice packs may not maintain -10C and colder thoughout a 24 hour cycle which includes night.

The only other solar option I am aware of is to revert back to older technology that relies on solar charged batteries to either operate a 12 or 24 volt DC freezer of use an inverter to power an AC powered freezer. I was hoping to eliminate the weak link in the system, the battery.

To date I have not been able to identify an SDD freezer among the mainline manufacturers -- Dulas, SunDanzer, SureChill, Vestfrost, Haier.

Thanks for any advice!


Claus Cording Accepted Answer

Hi everyone

This is a very interesting topic to be dissussed, what definetely also brings us as appliance manufactures, valuable knowlaged for our innovation and development within this area of equipment.

Important to underline for the PQS SDD freezers available today, they are not prequlified/testet as Vaccine/waterpacks freezers, but only as freezers hence just suiatble for freezing ice-packs NOT vaccines.

From our perspective it especially for SDD freezers, as also brought up eralier in this thread, would be appropriate if it could be accepted by WHO to re-implement the option for allowing using batteries again. It wuold grant by far a better performance for this kind of equipment, what in case could maintain the temperatures at the desired less than -15 degrees, needed for storing of vaccines.

At Vestfrost Solutions, we have a range of SDD freezers Type name SOE, that has been developed for the commercial, as well as semi commercial market, that operates by use of a battery. These freezers can do the job of keeping temperatures -15 degrees continusly during the day, have a proven track record and have through the years been installed  in various countires in Africa.

If any interest, do not hessitate to contact me.

Thaks´s to everyone contribution to this topic.


  1. more than a month ago
  2. Cold chain equipment
  3. # 1
HT Li Accepted Answer

Hi ,I am HT,  an engineer  from Haier.

 Maintaining below -8 is acceptable? AC is acceptable?

 We have AC type combined refrigerator and freezer, model HBCD-90:  the freezer compartment (gross volume 32 L) can maintain below -8 (environment: 32 )for more than 16 hours in case of power outage; the refrigerator compartment (gross volume 42 L)  can maintain 2-8 C, used for store vaccine. ( See the HBCD-90 test graph below )





Attachments (1)
  1. more than a month ago
  2. Cold chain equipment
  3. # 2
Larry Schlussler Accepted Answer

 Hi Dave

I think Stephen is correct, you will not find an ice pack freezer which will maintain temperatures of - 10 deg C.
As mentioned ice pack freezers are meant to freeze ice packs. We have a number of SDD freezers operating
in the Lagos area. Our design philosophy for our Sun Frost F 1 was to make the desired number of ice packs
with the evaporator temperature kept as high as possible. This keeps the efficiency of the cooling system as
high as possible and minimizes heat gain. To keep the freezer at - 10 deg C would require a different design
philosophy and as Steven mentioned phase change materials which freeze below -10 deg C.

What I would suggest is that you combine what you call older technology with new technology. Use an efficient DC freezer
combined with a power system incorporating lithium ion phosphate batteries. These batteries in a properly designed
system should give you at least 10 years. A well designed system would have an over sized solar array. This will
allow a smaller battery to be used and also minimize it's depth of discharge. If you need help with the system design I
would be glad to help. These batteries are a proven technology lasting 10 years or more in automobiles and
a car is a harsher environment for batteries because of vibration, greater depth of discharge, and high charge and discharge
rates. In the near future many of Europe's cars will be running on batteries.

For some reason WHO has resisted the use of these batteries. If someone knows the reason for WHO's resistance
please let me know. The incorporation of these batteries would result in highly reliable less expensive systems.
I would be glad to discuss this point further.

Larry Schlussler Phd
Sun Frost



  1. more than a month ago
  2. Cold chain equipment
  3. # 3
Steven P. Diesburg Accepted Answer

Hi Dave,

Nice work wading through and chasing down all of that information and pushing for real answers. Everything you said makes total sense to me and it's unfortunate that none of the PQS-prequalified equipment works for your application. Good luck, and I hope the system you've worked out funtions well!


  1. more than a month ago
  2. Cold chain equipment
  3. # 4
Dave Klassen Accepted Answer

Hello Steven,

This is all very helpful. I have spent the last month doing research and have spoken with engineers from B Medical Systems, Dulas and Vestfrost. I've had conversation wtih Africa Solar and Ian from Sure Chill. All of these individuals have given me very helpful advice. Essentially an SDD freezer that can meet the demands of a constant -10C or colder is not available at the moment. Dulas offered to build one for me and I encouraged them to do so, but that research and design work does not fit into my timeline. 

I have finally decided to go back to the more "conventional" solar panels and battery system. I have ordered a Steca PF 166H (at the recommendation of Ian from Sure Chill) and will be pairing it with a system of Deka batteries and Canadian solar panels, both of which are available in Lagos. The Steca is supposed to be a very efficient freezer that runs on DC power, either 12 or 24 volts. If you want to know more about the Steca, their web page has a significant amount of information and specifications on this unit in the way of downloads.

What I have learned is that SDD freezers are essentially designed to freeze ice packs. Even the volumes of those SDD freezers that are available, are defined in terms of the number of ice packs they can hold. Many are set up to "condition" the ice packs so they are just at 0 degrees C by the morning when they will be used. Even the B Medical Systems TFW 40 SDD, which was the closest to what we needed has a set point of -5 C and an autonomy (through the night) that would drop it to -3 C IF the unit was filled with ice packs. They made that last point very clear to me.

As I indicated earlier, the product we want to keep frozen is high value and low volume, so we cannot risk being exposed to several days of cloudy weather; the system must be more fool proof with resiliency and autonomy built in. I believe that a well designed and quality solar PV with battery power supply system will do that. 

The industry is not yet there but I believe in a few years it will be.

Thanks again for the input, feedback and advice!


  1. more than a month ago
  2. Cold chain equipment
  3. # 5
Steven P. Diesburg Accepted Answer

Hi Dave,

Glad you found the TFW 40 SDD. I was looking at the available equipment listed by PQS and there seem to be two additional models of SDD freezers that are prequalified along with a fair number of combined fridge/freezers. I'm guessing those combined units wouldn't meet your needs for volume but maybe some would. Your questioning of how long the freezers can actually hold -10C is a good one.

The verification testing of "autonomy" tests how long water-packs remain "fully frozen" in a given freezer. Autonomy being defined specifically in those documents as "Autonomy (freezer): Time in days that a solar direct drive water-pack freezer can maintain the minimum capacity of fully frozen water-packs under low solar radiation conditions (e.g. rain)." This testing isn't really directly applicable for your application because the metric measured is the test lab observing if the ice-packs remain frozen, not whether the temperature remains below -10C (or any other temp). My guess (and this is really a guess) is that the temperatures will hold more toward 0C when power is not available in these appliances. This is only because I am guessing that the thermal storage material they use to hold temperature when there is no power is water/ice. However, some companies may design there SDD equipment using a phase change material that freezes/melts at a lower temperature than water, which would then allow the freezer to hold at a lower temperature even without power input.

I'm attaching the PQS specification for SDD freezers in case you haven't found it already as well as the verification protocol. Specifically, Test 6 (secion 5.3.8) of the verification protocol might be informative for you because it specifies how autonomy is tested. Namely, the freezer still receives some "minimal" amount of power intended to simulate cloudy/rainy weather and evenings with no sun. I've also attached the 3 fact sheets from the 3 SDD freezers I found listed on the PQS website (which again you probably already found).

HTD-40 from Haier - 5 days autonomy

TFW 40 SDD from B Medical - 5 days autonomy

VFS 048 SDD from VestFrost - not list on fact sheet for some reason


Fact sheets are available as PDFs for download at this link:

Specs and verification protocols are also available at that link by clicking on the hyperlinked text "Category Documentation" near the top of the page (although the listings of the specification and protocl documents are a bit unclear to sift through).

I don't have any personal experience (in my work with PATH) with any of this equipment so can't give you any feedback. But I agree, seeing if the manufacturer can provide any performance temperature data and setpoint info, that should be at least helpful for you. Also seeing if they can tell you what thermal storage material they use could be helpful and what the freeze/melt temp of that mterial is (what temperature PCM they use would be most informative for you).

Good luck,



Attachments (5)
  1. more than a month ago
  2. Cold chain equipment
  3. # 6
Dave Klassen Accepted Answer

Update: I believe I have found an SDD freezer which will work -- the B Medical Systems TFW 40 SDD. I am trying to verify its set point temperature with the company. It would be great if there were anyone out there who could testify to their experience with this unit.


  1. more than a month ago
  2. Cold chain equipment
  3. # 7

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