Why is my circulation pump shutting off so early?

[Steeler.Fan]

image_12091.jpg171002 AKM Solar Thermal diag.jpg

I installed my solar domestic hot water in 2012 in a warm, rather sunny environment (11 inch of rain/yr). My system is complex because of a recirculation loop. I use a Heliodyne Delta T Pro controller (accepts up to 7 temperature probes & measures flow and energy production) to monitor my system online, remotely. My DHW system originally consisted of a 80 gallon electric hot water tank. My installer figured that I needed a 4x8' solar panel. The County only allowed me to have 120 gal of storage in order to qualify for their rebate program. Rather than throw out the 1 yr old electric HW heater, I opted to add a 40 gallon storage tank (80 + 40 = 120 gal). My production did not seem to be very great and I noticed that my flow was terminating around 12:30 pm and my energy started to drop even before then. I thought that circulation of water to my solar panel was stopping early because my storage capacity was too small. Therefore, I asked my installer to add a 100 gallon storage tank to my system, see attached layout diagram. That increased the amount of energy harvested from my solar panel and prolonged the pump circulation time (now stopping around 1:30 pm instead of 12:30 pm), see attached data chart from the last 24 hrs. Now I essentially have 140 gallons of storage for my 4x8 collector and an 80 gallon electric HWT as a back up system.
Although there is still plenty of sunlight until sunset (5:30-6:30 pm), my solar hot water production stops around 1:30 pm on most days. My solar hot water panel azimuth is 142 degrees.
Is this normal behavior or should I add more storage (replace 40 gal storage tank with another 100 gal tank)?
Thanks for any advice or comments!

[NewBostonConst]

Looks like system doesn't turn on till T1 comes down to 96 degrees and likely shuts off when T2 hits 150 degrees. 150 degrees is good and hot water.

Don't know if you could change the set points but I would first rise the 96 degrees on to like 120 degrees or more. There are safety things to with raising the temp in the tank from 150 degrees, but most tanks safety blow off valves are set at 210 degrees. Raising above 150 increases the chance of people getting burned.

If you can't change the set points.....Are you running out of hot water? if yes then add another tank. if no be happy with what you have.

[Steeler.Fan]

The recirc pump turns on when T1-T2 = set differential (adjustable value ?7F), turns off when different differential met (? 3F). It has been years since I set those differentials.

[LucMan]

image_12091.jpg171002 AKM Solar Thermal diag.jpg

I installed my solar domestic hot water in 2012 in a warm, rather sunny environment (11 inch of rain/yr). My system is complex because of a recirculation loop. I use a Heliodyne Delta T Pro controller (accepts up to 7 temperature probes & measures flow and energy production) to monitor my system online, remotely. My DHW system originally consisted of a 80 gallon electric hot water tank. My installer figured that I needed a 4x8' solar panel. The County only allowed me to have 120 gal of storage in order to qualify for their rebate program. Rather than throw out the 1 yr old electric HW heater, I opted to add a 40 gallon storage tank (80 + 40 = 120 gal). My production did not seem to be very great and I noticed that my flow was terminating around 12:30 pm and my energy started to drop even before then. I thought that circulation of water to my solar panel was stopping early because my storage capacity was too small. Therefore, I asked my installer to add a 100 gallon storage tank to my system, see attached layout diagram. That increased the amount of energy harvested from my solar panel and prolonged the pump circulation time (now stopping around 1:30 pm instead of 12:30 pm), see attached data chart from the last 24 hrs. Now I essentially have 140 gallons of storage for my 4x8 collector and an 80 gallon electric HWT as a back up system.
Although there is still plenty of sunlight until sunset (5:30-6:30 pm), my solar hot water production stops around 1:30 pm on most days. My solar hot water panel azimuth is 142 degrees.
Is this normal behavior or should I add more storage (replace 40 gal storage tank with another 100 gal tank)?
Thanks for any advice or comments!

I'm going to say that it's your SE azimuth if your azimuth were closer to 180 your panel would be harvesting more BTU's. I have the same issue with my 3 X 28 sq ft panels at 142 degrees my pump turns off at about 12:30 pm this time of year, May June and July 2:00-2:30.. Your limited to the production because of the angle the sun is hitting your panels and the height of the sun. In June when the sun is at it peak you will notice increased production. Here's a solar irradiance chart. I f you want more HW add another panel.

[Steeler.Fan]

As my graphs indicate, at 1330 or 1:30 pm, my flow to my panel cuts off despite the fact that the panel stays hot until 5 pm. So even at 142 degrees azimuth, I still have plenty of solar energy in my solar panel until later in the afternoon but I can't harvest it. The flow cuts off because the temperature of my storage tank water is too high and I lose the required temperature differential. If I add another solar panel, I think that I will lose the temperature differential sooner. While my flow to the solar panel stopped about 1330, the energy that I collected began to drop much sooner (around 11 am) as my storage tank temp rises, see energy graph.
190316 AKM T1 T2 Energy 24h.jpg
190316 AKM T1 T2 Energy 24h.jpg

[NewBostonConst]

Is it a convection system or is it primed by the pump?

I still really think the pump just needs to stay on longer. Most pump are 120 VAC and you bypass the controller and just power it longer to see if if gets the temp up higher?

Also your set points for turning on and off the pump need some work because at 7:00pm the tank hits 96 degree and the pump appears to turn back on and starts heating the tank back up and is able to a little till the sun goes down.

[J.P.M.]

As Lucman notes, but depending on your tilt, the system will not run as long into the afternoon because of the 142 deg. azimuth.

But, silly question - what about the sensors ? I'd check both of them, particularly the collector sensor. Not so much that one/both will go bad (but a possibility), but that they are not affixed to their heat source or insulated in the same fashion or with the same level of insulation. You want sensors that are operated in the same fashion under as close to thje same environments (except temp.) as possible. That means senmsors similar in type and affixed the same way to a pipe of the same material type and size, and perhaps most impotantly, well insulated or at least insulated with the same insulation material of the same thickness.

Reason: If a sensor has poor thermal contact with it's temp. source, or if it is poorly insulated - or insulation that's non water impervius that's failed due to getting wet, or any insulation that's been removed or otherwise compromised in some way, that sensor will report a lower temp. than if that sensor is in good thermal contact and/or will insulated.

If that's the case, and the sensor is the one that reports T1, then to the extent that sensor reports a lower temp., that reported temp. will be closer to T2 at the tank outlet.

If the T1 sensor thinks the water is lower in temp. because T1 has had it's insulation compromised, or it's somehow lost good thermal contact with its heat source, or both, with the result that the perceive temp. is what the sensor reports to the controller, the controller will then see a lower differential temp. (T1-T2). That will cause the controller to turn the pump off sooner (and probably start it later as well) than if the T1 sensor reported a more accurate (higher) temp.

I'd check the T1 sensor fixation, and wiring, and the insulation level/condition. Make the insulation heavy and waterproof and impervious to UV by wrapping in foil tape, but in any case, the make the sensors, their fixation, insulation and operating conditions as identically the same as possible for both sensors.

An example for illustration only, but to my experience using reasonably probable/possible numbers: If the insulation on T1 loses, say, 10% of it's original insulation value from weathering (and also while the assumed inside and unweathered T2 sensor conditions are mostly unchanged), and while keeping good thermal contact to the pipe it's attached to, T1's reporting temp. will drop. For a 10 % loss in insulating value loss from weathering, and to a first approx., that sensor temp. drop will be ~~ 10% of the temp. diff. between the water temp. at T1 and the ambient air temp. If that's the case, and if that delta T is, say, 150F (collector outlet temp.) - 90F (ambient air temp.) = 60F, then the sensor will report a temp. that's 6F less than if the insulation/fixation was in it's original condition.

Bottom line: For any number of reasons, maybe part of the problem is the sensors and/or how that are reporting the system temps. Has anyone who knows what the above mental spoor is all about taken a look at the sensors ? Might be worth a sniff .

One other comment. I think there's something amiss w/ Lucman's graph. It needs info about lat./long. and surface orientation. It can't be for global horizontal insulation and have a peak at ~ 1400 hrs. It also can't be for a surface at 142 deg. az. and some (??) surface tilt to the horizontal and show a peak in irradiance at ~ 1400 hrs.

If you want good/better performance, before you get another collector, I'd at least consider getting the sensors checked out, and if you want a better designed system, increase the collector storage loop to 100 or 140 gal. and rearrange/add flexibility by valving to get the collector operating temp. closer to the desired use temp. Then, I'd get a Rotameter to measure the flowrate, and probably get a bigger pump to increase the flowrate through the collector to ~ 2 GPM or more, or at least get the flow into a transition region to turbulent flow. (Maybe) Unfortunately, while bumping the flowrate has a lot of advantages to improve system performance, doing so will involve fooling around with the signal from the sensors to fool the controller into thinking the temp. diff. is more than what it is. FWIW, I run at ~ 4 GPM in series through 2 ea. 4 X 8 collectors. The system runs ~ 9 -11 % more efficient in terms of annual production than if running in deep laminar flow at, say, 1 GPM. Been running 11 yrs. and only replaced an O ring on a flex joint and kept an eye on the pipe insulation (1" closed cell Armaflex, foil wrapped) and sensors, with 2 yr. maint. changeout for air bleed and PRV and ~ 5 yr. changeout for all the ball valves.

Take what you want of the above. Scrap the rest.

[LucMan]

JPM it's just a general graph under optimum azimuth and tilt conditions, used it to illustrate the time of year performance differences. The true performance of the panel would need to be calculated using Solar Pathfinder or equivalent software with the actual panel model, GPM, azimuth, tilt , Longitude, Latitude and shading and or fouling.

[J.P.M.]

JPM it's just a general graph under optimum azimuth and tilt conditions, used it to illustrate the time of year performance differences. The true performance of the panel would need to be calculated using Solar Pathfinder or equivalent software with the actual panel model, GPM, azimuth, tilt , Longitude, Latitude and shading and or fouling.

Optimum tilt and azimuth conditions for who ? You ? the OP ? Anyone ? Without a bunch of qualifiers and caveats, that graph and presenting it here, and in that fashion, is misleading, particularly IMO, for someone like the OP who seems to not have the level of solar knowledge necessary to understand how misleading that graph is, particularly for his situation.

I appreciate what you write in the above post as to what's necessary to estimate or actually calculate solar device performance every bit as well as you do, and I agree.

My comment was made because to publish that graph in the way you have done has done nothing to clarify the situation for the OP, and maybe made it more confusing. Also, the way it was presented makes that presentation open to criticism as being inaccurate, confusing or simply wrong.

I believe you're one of the more knowledgeable posters around here, especially with respect to solar thermal, but in this case, and IMO only, you usually do a lot better than this.