OP
steve k
So running at sub zero ambient temperatures, the panel will ice up?
I have seen them icing up at 6 deg C ambient. Remember the gas in the evaporator is at -12 deg C.
Discuss Thermo dynamics for hot water that runs off atmosphere in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net
So running at sub zero ambient temperatures, the panel will ice up?
that would be stagnation temperatures though, ie when the compressor wasn't running, and that would be extreme top end. tbh I've never known PV panels to get anything like that hot in the UK, usually more like 50-55 deg top end due to the air cooling which this will also have. Thinking about it some more, I'd expect these panels would stagnate at a lower temperature than that due to it's greater surface area (fins) and conductivity to the rear of the panel for greater cooling of the rear (back of a PV panel can be around 35deg while the front is at 50 due to the poor conductivity, I'd expect this to be far more even in an aluminium panel, so the heat loss to air on the back would be that much greater).60-70 deg on the evaporator is very very high compared to standard refrigeration systems. The negative effect this will have is on the compressor, not the refrigerant itself. I would have grave concerns about the the long term reliability of this system.
In operation I'd be surprised if it ever went much above 25-30 deg flow temperature into the compressor even in full sun, though this depends on the flow rate and return temperature.
From your reply, does in your opinion this mean there is a minimum ambient temperature at which this equipment should operate?
Actually I reckon that where used for water heating only at least it doesn't need a defrost cycle, as it's probably simpler and more cost effective to just switch to immersion if required once the COP becomes lower than 1:1, then rely on the sun to defrost the panel - this is one advantage these systems have over ASHP where the sun will never defrost the ASHP while outdoor air temps are low, whereas I'd expect the sun would be able to defrost these panels fairly quickly even in -10 ambient air temperatures, which I've certainly seen happening with PV panels.Its is good to see some more technical discussion of this technology, even without firm performance data. At the other end of the scale, how is this equipment going to avoid icing and what defrost cycle is available?
not entirely true - the electricity to power the pump can easily cost £5-10 a year depending on the set up, efficiency of the pump etc. Unless it's a PV powered pump, or I guess if the customer also has solar PV installed.The running costs element is critical to its viability. Normal Solar Thermal has zero costs for energy production and pretty low running costs - a fluid change every five years and a pump if you are unlucky during it's lifetime.
snigger... the same numpties who killed the solar thermal industry immediately the tory government got into power by pulling the plug on the previous grant scheme then taking 3 years to fail to implement RHI? That's not my definition of hard work to make ST viable, quite the opposite, but yes maybe they will eventually come up with something that makes it viable again.There is a lot of hard work going on with DECC to make normal ST viable under the proposals for the RHI.
I agree that it should be a niche product,but I'm not sure I'd agree on the size of the potential niche being 'very small'.I think the one thing the opinions expressed in this thread shows is the true market for appropriate use of this equipment IF it's performance can be validated is very very small.
that entirely misses the advantage these systems have over solar thermal in that they do not need a secondary heat source other than an immersion for the very few days of the year when the system can't operate due to extreme low temperatures. So no they don't need a second coil to be combined with another heat source.Use in conjunction with other technologies means it would need to to be compatible with a multi-coil thermal store or hot water storage vessel, not just a dedicated tank. If it is not compatible, you are possibly in to a two tank design, with all the space implications that entails.
yes, but they are insulated from the air, this panel is specifically not insulated at all, quite the opposite, it's highly conductive to air as it's entirely made of aluminium.ST panels get way hotter than this during stagnation, hence the avoidance of soldered joints. Temperatures can exceed 180degC.
oh erm, right, sorry I've not hugely looked into the exact functioning of the heat pump side of things, tbh I don't think I've seen a proper diagram of how they're laid out, and I've not actually worked with heatpumps (at least not the internal side of them).If you ever saw this kind of temp flowing into the compressor, you need to call a fridgeman. Your expansion valve is knackered.....
the compressor doesn't create heat*, it merely concentrates it from a lower grade to a higher grade of heat. The original heat energy input that allows for the high COP's comes from the panels extracting heat / energy from the air and solar radiation.The thermo dynamic panels only require small amounts of heat to operate, the heat comes from the compressor to warm the water, not the panel.
basic laws of thermodynamics say you're wrong.not if your using gas it dont
I'm fairly obviously not saying that the compressor doesn't extract the heat energy and boost it up to the required temperature, but you seem to be denying that the heat energy actually has to originate in the panel, which is obviously wrong.The panels wont reach 55 degrees if the outside temp at night is -5. Thats why ASHP can work down to -20,
Absorbed Power 0,9 - 1,8 kW ; Thermal Power 3,6 - 7,3 kW
it's not a matter of degrees as such, it's a matter of total energy input into the system. and yes you could put the panel in a lake if you had one, but this is an alternative for those of us who don't have sufficient lakes or ground for a GSHP / WSHP to be an option.Yes but only a few degrees, stick the panel in the ground or lake it would still work, how do you think fridges work or cold stores, freezes.
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