Guidance needed - In floor Radiant heat

Jorgy

18 year old Minnesota One story 4” Slab on grade with insulation underneath and at the edges, R38 attic/R19 walls, 4 zones/4 thermostats, 3 year old HTP boiler, closed loop with primary and secondary piping, 1/2” hePex, spacing unknown but maybe 9-12” from photos. Primary loop has Taco007, secondary has two Grundfos single speed pumps 1/6 hp UP 26-96 and the other a UP 26-64. 4 Uponor TruFlow Jr brass manifolds, 2, 3 and 4 loops. Boiler temp supply around 120. Solar gain keeps things shutdown until evenings during 30 degree weather.

Heating effectiveness seems to be slipping over time. Worst performance is at the end of the house which is the furthest from the boiler and pump. I’m trying to educate myself and understand the system in an effort to improve the situation or possibly protect myself from the shotgun approach of A FEW contractors, should I choose to get them involved.

The builder or heating contractor never gave us any heat loss numbers or system calculations, length of tubing on the design. However I do have the house plans. I have photos from build that generally show the 1/2” hePex that was installed but not specific enough photos to show the exact routing to determine length of circuits, etc. I installed some .25 - 2 gpm visual flow meters on the manifold for the end of the house that is problematic. I don’t know head pressure and don’t have the lengths of the circuits so I can only guess which loop is longest. I’ve been doing some experiments with flow rate, checking delta across the zone and across each loop with a temp gun. I’m around 119 supply, 105 or 106 return. My current experiment has .8 gpm on each circuit and
the rooms are at 65 and 66 degrees with it 2 degrees outside, never achieving set temp. Can I back my way into understanding this system by using the floor plans, calculating heat loss, head pressure and figure out if my pumps are too big or small, or do I have to go that far? Can anyone provide me nexts step suggestions? I just got the RadPad last night to see if I can figure some things out. Thanks for any wisdom and thank you already for the significant education I have already gotten. I appreciate you!

hot_rod

A drop if performance over time sometimes indicates a reduction of flow in the system 
Is there  a filter or Y strainer in the system?
Recently a system here had a plugged air purger, the brass  Spirotherm device on your system could be partially plugged. It would be one of the  first things to look for.

GroundUp

All 3 Grundfos pumps are much bigger than they need to be, but that's of little consequence. Are these 119/106 temps being measured at the loops or at the boiler? With a 105-106 degree return temp on all loops, if they are indeed flowing .8 GPM each (which is normal or even high for a typical 1/2" pex loop), the slab should be hot underfoot. Like, 100+ degree surface temps. That's approximately 5200 BTU per loop being radiated, so there is a shortage of either tubing or insulation- most likely the latter. What sort of floor coverings in these troubled areas? You say nothing runs until evening due to solar gain, but are also saying that the system never catches up. Is it running 24/7 or only from evening to morning? Also which part of MN are you in? I am in MN myself and could possibly run some diagnostics if necessary.