Analyzing solar + heat pump performance/configuration

[carlscan26]

Matt,

In looking at the pics I see two places where the hot water exit from a panel needs to be moved from what they are showing (possibly not a problem and just the way they drew the pics):

You always want to see water egress at the opposite high corner from the ingress. I highlighted the panels in yellow and put red arrows where I think the egress should be.

 

[MattM]

Current schedule:
Deep heat returns active at begining and end of day
intellichem starts measuring water ph/orp at 7:40am, and begins dosing around 8:10am...continues to 7pm
pump on from 7:30am - 7:30pm
solar preferred heating from 8:45am-6:30pm (fails over to heat pump if solar temp isn't at least 5 degrees above water temp, won't restart unless solar temp is 9 degrees higher)
Usually solar goes on immediately and stops around 4pm, and then heat pump takes over until 6:30pm (air temp usually remains reasonable until about then).
The temp sensor is currently facing towards the south.

Good point about ensuring that all water drains from the panels at end of day...that is the intent so that we don't have to worry about programming a freeze mode/etc...most of the water seems to drain right now but I'll talk to them and see if any panels are not draining

We've been doing some data gathering the last few days and measuring how effective each of the panels are and which are really filling up/etc..

As far as solar pump speeds:
2310 rpm is enough to get water onto the roof and maintain a minimal flow -- however most panels do not empty of air
2400rpm gets most panels into operation, but it might take all day for all the air to come out
2500rpm gets nearly all panels into operation in reasonable time, but there is still air coming out for a long time and at least one panel that never works properly
2650rpm is much faster at getting air out, but doesn't really add anything

So, we're running at 2500rpm now, but hot sun industries thinks after we redo plumbing and add panels that we may be able top drop the pump speed a few hundred rpm...and that in a good system, air bubles shouldn't last more than a few minutes.

 

[carlscan26]

Adding panels but reducing speed? That doesn't sound right unless they think that the reconfiguration will more than make up for the additional panels to push through.

 

[Brentr]

I wonder if the panels mounted on the north side of the house are not contributing to adding heat. In fact it might actually be cooling off the temperature. Can you do an experiment by disconnecting then and just running the rest separately? Check the out coming temp with and without them connected? You should be able to check the temperature of the water out flow of the panels on your heat pump if the heat pump is plumbed after the solar panels. Just a thought

 

[MattM]

See below for panel temps (blue indicates incoming water temps, red indicates temps while solar runing, stagnant = temp when solar not on):

 

[carlscan26]

So what did they recommend?

It looks like for sure you will wnat to ditch the panles on the North side. You said previously it wouldn't be worth the effort to remove them but what if you left the brackets etc. but pulled the panels off and put them on e-Bay? I guess if they don't bug you up there then who cares?

How did they gather all this data? Were they up there with a laser thermometer or did they actually place thermometers and run them to a laptop or recording device?

 

[MattM]

Proposal we received is to redo all plumbing and a) keep panels on north as is since they aren't having any significant negative impact and would become positive in summer but also add panels on southwest corner immediately (~200 sqft) and if needed saturate west side with new panels (powerstrips that would fit the triangular shape nicely). It's a little frustrating to pay for more work after the poor job the prior company did (we've filed a BBB complaint) but the recommendations seem reasonable to me.

 

[MattM]

Update:
- Plumbing has been redesigned/rebuilt to ensure optimal water balance/flow to all panels
- 200sq ft of additional panels were installed in the southwest corner
- panel temps, temp sensor, and pump speeds were tested/verified were reviewed before and after changes.
- The techs at hot sun industries spent effectively almost an entire week with 2-3 guys performing the necessary changes and testing various performance improvements. They're still scheduled to come out again to see if we can get the pump running slower and ensure the system performs well even on a very hot day and repair a few tiles on the roof. Earlier tests showed that can get water flowing all the way to the roof at just 2100rpm.

End result: The temp sensor is also now reporting higher readings and generally turning on heating earlier and stopping later. We're getting water through ~712 sq ft of panels at 42gpm on a tall 2 story house at approx 2300rpm with water that is at least 5 degrees warmer than pool temp even on very cool days (low 60 degree air temps). Solar today ran from approx 8:45am to 5pm (9.25 hrs). Heat pump utilization is greatly reduced.

Weather was poor this week, so I didn't get a chance to see how much it could heat - but this weekend is to forcast to almost reach 80 degrees. We'll see what it can do.

 

[carlscan26]

Nice! What did you mean they did some tuning to still work well on very hot days?

 

[mas985]

Matt,

If your primary objective is to reduce the run time on the heat pump, then you might want to increase the flow rate through the panels. A 5 degree temperature rise in the panels means you will be losing a lot of heat to the environment especially when the air temp is 60 degrees. If you increase the flow rate, you will have a lower temperature rise in the panels, lose less heat to the environment and have a higher heat gain in the pool. Each section should have about 0.1 GPM/sq-ft to maintain high efficiency so you should be closer to 70 GPM. But you have to decide which is better lower pump RPM or lower heat pump run time.

 

[MattM]

The goal with evaluating performance on hot days was to ensure that all panels are heating up evenly and if not, reduce or increase flow. We're still using the north panels, but they are now only getting about 20-25% of the flow the south panels are receiving.

Anyhow, on an 80 degree day, we had an 8 degree rise from pool to roof and on a cool day the lowest rise is 4 degrees at @2300rpm. Pool water temp briefly touched 81 degrees over the weekend and otherwise has been oscilating between 78-80 degrees so far this week.

We can get the water up to the roof at ~2100rpm but it doesn't start up fast until ~2200 rpm and ~2300 rpm seems to be the best compromise of heat transfer, clearing air out of panels, pump energy, and pump noise. 2300 rpm is only ~13 psi on filter and intellitouch says 700 watts while flow meter reports ~40 gpm.

Heating schedule has been setup so on very sunny summer days the heat pump will not run at all, on a standard or sunny winter day for <1hr, and on those rare rainy days in san diego for a full 9hrs.

We just got our first pool electric/gas bill....it wasn't that bad..we normally run ~$200 and it was for ~$350, so $150 extra during the first month which included heating the pool up from 50 degrees to 75 degrees using combined heat pump/solar/cover.

Techs brought down electric sensor cables from each row of panels on the roof and said I could put volt meters on them to check temps of each going forward.

 

[wildta]

The goal with evaluating performance on hot days was to ensure that all panels are heating up evenly and if not, reduce or increase flow. We're still using the north panels, but they are now only getting about 20-25% of the flow the south panels are receiving. .

I'm curious to hear any updates you might have regarding your system. I'm in San Diego as well and looking into a similar idea of heatpump and solar. Really interesting thread.