Need an expert statement - Page 1
Forum section: electronics / general

author: Sauli
author_rank: Contributor
timestamp: February 11, 2022, 02:21:37 pm
content: Perhaps I should have put this in the Jobs board, but the General Technical Chat board seems more active..I have at home an air-to-air heat pump. One of those with an outdoor compressor unit and an indoor heat exchanger unit. About 1.5 years ago the indoor unit was replaced. This was covered by the quarantee. But the next winter it turned out that the device stops heating when the outdoor temperature drops below -15 degrees. The company who sold/installed the the unit tried to diagnose/solve the problem on several occasions during the winter. The last thing they did was change the electronics control board of the indoor unit from the one intended for middle European market to a one for Nordic market. However, this was so late in spring that there no longer were cold enough weather to cause the heating to stop.Last Decebmer this control board change proved to be useless, the problem remains.Now we are at a point where I have raised a dispute with the seller. The problem is that since the quarantee has expired it is my responsibility to prove that the device is not working correctly. In addition to the seller questioning that there is any problem with the device he is claiming that that any problem is self caused because I have modified the device.And now we are getting to the cause why I am writing this message. So, I must be able to prove two things:1. That the device stops heating at cold weather.2. That it is not caused by my modification.Perhaps worth mentioning that it makes no difference whether the indoor unit uses it's original NTC sensor or my modification. Heating works just fine unless the outdoor temperature is too low. The seller claims that the modification has broken the indoor unit electronics in such a way that causes this behaviour.The modification is that I have replaced the NTC indoor temperature sensor of the indoor unit with a programmable resistance. The purpose of this modification is to move the measure point from the indoor unit to the living room area where we mostly spend our time. This is about 5 meters from the indoor unit and the measure result is transferred by radio to the indoor unit where I have added the necessary electronics. Now I need a qualified electronics engineer to give an expert statement about how probable it is that the modification has done some damage. I know a couple ones myself, but they are deemed biased just because I know them. I have also contacted several companies here in Finland who write expert statements to insurance companies about household appliances, but they all have refused or ignored me. Perhaps they are not much of electronics experts. Not knowing where to turn next, I decided to try this forum for help. So, if there is anyone willing to give a statement, please let me know. I will provide documents for the basis of the statement. And you don't have to give it for free.

author: Carel
author_rank: Regular Contributor
timestamp: February 11, 2022, 02:53:11 pm
content: I am not an expert, but I remember the stopped functioning of a refrigerator in a shed of a neighbour during winter. After scratching my head and Googling it turned out to be an indoor refrigerator. The filling gas/fluid is different.I am such an expert that I had to Google air to air heating:https://www.daikin.eu/en_us/product-group/air-to-air-heat-pumps.htmlAnd yes, if I had a heat pump, it would be useless for you. (lower on the page, optimised heating 4).So far, my non-expert opinion.

author: jonpaul
author_rank: Super Contributor
timestamp: February 11, 2022, 03:12:50 pm
content: Bonsoir monsieur Monsieur good problèmeNeeds photos and block diagrams of entier systèmeA few questions pleaseWhat's the cost of the entire installation?Did you read all terms of,sale and warranty?How much does a lawyer in your area charge per hour?Normally any manufacturer warranty is void if the unit or installation is modified.Could your different temperature sensor and wiring affect the control board?Bon chanceJon

author: dietert1
author_rank: Super Contributor
timestamp: February 11, 2022, 03:54:09 pm
content: At how low temperatures do you want to use the unit? There will always be a technical limit.I think in a dispute about engineering, one needs recorded measurements as a base for reasoning. In this case probably logs of machine states (temperatures inside/outside, power consumption, pressure whatsoever). Does the coolant freeze below -15 °C? Is there snow/ice covering the outdoor unit? Can the electronics provide these data?For our photovoltaics installations i once bought a 2x serial to ethernet converter to grab the data and feed them into our network. In Germany there are no real winters anymore, no more snow, rarely below -10 °C.Maybe the company can also provide those logs, better avoid another dispute.Can you undo your mod until the problem is clear, maybe get the inhouse box replaced by the company?Also you could try to find an alternative product and in this process get some idea what may be wrong with the existing one. Are you the first one in town to try that heat pump? Maybe a small roof above the unit could help.Regards, Dieter

author: coppice
author_rank: Super Contributor
timestamp: February 11, 2022, 04:05:53 pm
content: Quote from: Carel on February 11, 2022, 02:53:11 pmThere are lots of problems with fridges and freezers in cold conditions. Most models have a note saying they are not suitable for use in sustained cold conditions, but they don't usually make this note prominent. They aren't talking about Siberian conditions, either. Many say they are not suitable for sustained operation at <10C, once you have found the detailed statement. If you intend to site a fridge or freezer in an unheated location in a cold country its best to check for an explicit statement about just how cold the site is allowed to be.

author: tom66
author_rank: Super Contributor
timestamp: February 11, 2022, 04:08:30 pm
content: Quote from: coppice on February 11, 2022, 04:05:53 pmA fridge-freezer in a garage is a common issue.The fridge continues to keep stuff cool because the room temp drops below 5C but now the freezer doesn't get cycled enough to remain cool.

author: coppice
author_rank: Super Contributor
timestamp: February 11, 2022, 04:16:22 pm
content: Quote from: tom66 on February 11, 2022, 04:08:30 pmYep, that is an issue with most reasonably priced western half fridge/half freezer designs. They only have one heat pump, and no control mechanisms to selectively apply cooling to the freezer or fridge section. Asian models tend to be much better. They have fans to circulate the air, which are selectively applied to reduce the problem. However, many chest freezers, which are frequently sited in sheds are garages, also have a low environmental temperature problem.

author: Cerebus
author_rank: Super Contributor
timestamp: February 11, 2022, 05:04:33 pm
content: Is it a single stage or two stage system, and what refrigerant gas(es) is the system charged with?i.e.The first job is to determine that the system is actually capable of operating at sufficiently low outdoor temperatures and wasn't grossly misdesigned/specified in the first place before we start blaming the control electronics. Has iteveroperated at circa -15ºC outside temperatures?

author: TimFox
author_rank: Super Contributor
timestamp: February 11, 2022, 05:10:21 pm
content: At the first location (ca. 1985) of my former employer (I am now retired), we had an old-fashioned computer room at the center of the office suite that required air conditioning. We had serious problems in the winter, where the roof-mounted unit would not work at common outdoor temperatures of -10oC.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 12, 2022, 08:09:12 am
content: Even if you get such expert opinion, they can just choose to ignore it. I could do it but I doubt it would be of any help, and they can always just question my formal qualifications, simply because such formal qualifications to write such statement simply do not officially exist.Assuming that product specifications (brochure shown to you when you bought the unit) actually specify operation well below -15degC, I guess your best bet is1) consumer protection authorities,2) media,3) social media,or combination thereof. It's amazing how much a negative article in press, or a tweet, can do with companies who refuse to perform their legal obligations.Fixing issues, by installing a completely new unit if that is what's needed, is normal business operation and covered by sales margin and installation costs. Besides, sales profit and install costs of air-to-air heatpumps in Finland have gone up so much you can actually buy 2-3 units installed, in most other countries. But this sure can't be seen in install quality or guarantees.

author: jmelson
author_rank: Super Contributor
timestamp: February 13, 2022, 03:00:37 am
content: An air-backed heat pump will certainly not work well at -15C without using electric resistance heating. Does the air handler (indoor) unit have this? Is the electric resistance element properly sized for the load? It will likely need to be pretty large for a typical home at that outside temp. Somewhere around 10 - 20 KW is likely the minimum requirement.Jon

author: Siwastaja
author_rank: Super Contributor
timestamp: February 13, 2022, 07:54:30 am
content: Quote from: jmelson on February 13, 2022, 03:00:37 amThis is just BS.Modern models work really well at -15degC. Doesn't even need to be that modern. State-of-the-art machines 20 years ago could already do it.With indoor fan set at maximum to provide lowest possible condensation temperature, COP can even exceed 2.0 in a well designed machine! It's still far from resistive heating.-25degC is a different story. Many products continue operating even to -35degC, but COP reaches 1.0 even before that, equivalent to resistive heating, in which case it's a matter of taste whether you turn it off to "save on operating hours" (but keep wasting some 50W in compressor heater), or keep it running.