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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!


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. 2019-01-16 16:00:28
  2. Cold chain equipment
  3. # 1
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. 2019-01-07 14:30:55
  2. Cold chain equipment
  3. # 2

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