View Full Version : Help me please ..... Solar heat pump lagging !!

30-11-2012, 08:48 PM
Hello can some body tell me why you need to lag the external ( outside of building) liquid and suction pipes on a solar thermal unit ... Surely the idea is to gain as much "heat" through the wall or roof mounted evap panels and surely the pipe work as well...
If we lag the pipe work we are limiting the amount of heat transfer to the hot water through the heat exchanger ??? Any ideas .... Inside the building we understand as the blocks are fitted with expansion valves hence the " evap " line needs lagging but surely not when it's gets outside ?....

30-11-2012, 10:57 PM
The temperature of the fluid inside the external pipes will be much higher than the ambient air. If the pipework is not lagged then you will be loosing heat from the system, not gaining it. A solar panel can very quickly raise the fluid temperature to above boiling temperature if there is no flow for example.

01-12-2012, 07:24 AM
Just a flat static coil or 2 on the roof is your evaporator? Neighbours of mine had one some time ago and neither pipes had insulation on them. Insulate the suction line so that you can bring cool gas back to the compressor. Too much super heat and your compressor will run hot. Condensation is another reason.

01-12-2012, 10:21 AM
Roof has 18 evap panels with a main 3/4 liquid line and 7/8 suction with a pre constructed distributor (liquid) the problem we have is on a sunny day it's fantastic no liquid slugging as there is enough ambient heat to keeps pressures up and refrigerant boiling off but in winter with -3 deg c running r407c back pressure is 30 psi at best and very low discharge pressure and heat ... Hence we have not lagged liquid or suction outside to simply gain as much heat as possible from the ambient air .... Currently x2 scrolls frosting up with system perfectly charged .... Super heat is very low as you would expect ... Can some one turn the sunshine back on please .... Surely to lag would make things worse ???

01-12-2012, 10:30 AM
It's the reverse problem it's minus 3 deg outside we can't get enough discharge heat to the heat exchanger as pressures are so low put it this way if you upped the outside ambient temp as the system is now ( not lagged ) its workers fine ... Fixed tev inside condensing unit currently lagged both pipes inside the building as they frost which is all good ... It's just not boiling off as well because its so cold .... So lag or not lag ?