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Joined on August 20, 2009

Last Post on February 28, 2014

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you're still

@ May 28, 2013 11:36 AM in Solar Thermal is Dead

limited by the btu collection of the thermal in that case... all it does is improve the heat pump COP for a portion of its usage related to that number of BTUs. remember heat pumps do not create BTUs, they only move them. so your heat pump in that case isn't helping much.

without any subsidy right now PV has about a 15 year payback by itself here in maine. the net metering is an issue if it went large scale, but there are many, many ways to work with that. also:

1. PV collection is strong during peak electrical usage periods (summer cooling period, even here in maine). if/when the peak shifts to heating periods (winter nights) that may change but for now blunting the peak demand with solar production is a big win for the grid that greatly offsets any additional cost for handling net metering administration.

2. Thermal energy can easily be stored in tanks. there are ETS systems out there as well but I think tanks will be the big winner. right now I run a heat pump time shifted by using my lower level slab as a heat battery to maximize COP but could do it to maximize electrical economy just as easily to take advantage of any time of use metering solution anyone wants to dream up, and those schemes are in the works because the utilities know this is all coming. Smart meters exist right now in every home in Maine even though those TOU plans are still in their infancy here, they are ready to go.

Like it or not the grid is going to have to deal with intermittancy. What is clearly unsustainable is a long term focus on unsustainable energy sources, not the economics of renewable energy long term.

that's great

@ May 20, 2013 10:48 AM in Solar Thermal is Dead

that you're happy with it. but you're an industry professional getting a 20 year payback. retail that's what, 30 years? non starter. No one in their right mind pursues a 30 year payback... there are endless other things you could do with that money with better economics and with better energy savings to consider.

PV is about a ten year payback in the northeast these days just on the federal credit, 15 without... and that's still a stretch for most people. My heat pump is a ten year payback or five if it saves me a boiler, with no credits at all... unless you're in a natural gas situation, of course, since it's so cheap these days.

So you just proved it makes no sense whatsoever to pursue solar thermal for space heat. I know your system is older and PV was more expensive when you did it. but things have changed. Why would you ever do thermal for space heat now, when PV is so much more effective at offsetting your energy use?

I socked away almost 4 million BTUs last month to use later when I need it. My heat pump will double that to 8 million+.

I have no idea

@ May 13, 2013 11:25 AM in Solar Thermal is Dead

what you are talking about with your "excuses" comment, but I'll assume you aren't trying to insult me, since I did, in fact, spend my own money to see what works. I'm net zero, remember?

If you have a storage tank that can allow you to shift your solar collection above and beyond your DHW needs from April through october into your heating season, then great. I'd love to see the specs on that tank.

Until then, I have about five or six months of solid, high output solar collection that you don't get to utilize like I do, because I went PV. If you want to wave your hands about collection efficiency, I'll simply point this out...
go ahead and see what you've got, month by month.

I just ran this for Augusta Maine. I have heating demands from November into April. But let's be nice: I'll let you use every KWH available from October through May (I have a very tight shop, most homes need more heat than i do) and just assume you don't lose any at all, you use it all. In Augusta, that's an average of 2.54 KWH/m2/day or about 210 KWH/m2 for the seven months. you're about 60% efficient and so that's 126 KWH/m2. You don't get to use any solar in any other month for space heat, only domestic, which we can agree is a tiny load compared to space heat, right?

I'm PV. Let's say I'm 10% efficient. so I only get 21 KWH for the same seven months you do... but, I can drive a heat pump which doubles it to 42 KWH/m2 applied to my heating. However, the OTHER five months a year give me about 723KW/m2 gross... ten percent and doubled gives me another 144KW/m2.

So I can run 186KW/m2 for heating with solar. with solar thermal you can only do your 126. I'm 50% higher by area, and that's still give YOU may in this comparison.... realistically we're being nice. Plus I can apply it to cooling, DHW and power and not just DHW or space heat, if my loads are too low.

this is by area though, the real question is cost. So, how much area does your system cover with panel, and how much would it cost retail before credits? We can do this with math Bob. it works.

it's "one"

@ May 11, 2013 11:30 AM in Solar Thermal is Dead

because one makes a lot more sense than the other. solar thermal has poorer economics for space heat. Unless you can do it damn near free.

if you can get solar PV in for $2/watt PRE TAX CREDIT, then the discussion is completely over (though here in maine it's not that cheap). taking up roof space for hot water panels past the DHW demand is then seriously a waste of time and money and at $2/watt I'm not even sure solar thermal for DHW makes much sense when you can do an electric water heater tied to PV. at $3.50/watt PV was already compelling for space heat. Heck, at $2/watt, and 0.15/kwh electricity, you're below a ten year payback on PV with no credits at all. If that's after credit then it's pretty much the same as my cost last year.

Seriously... name an installed price and a yearly expected BTU delivery for a solar thermal system. anything you want to run through polysun or any of the solar calculators out there. we can compare this very easily. I just can't do solar thermal collection calcs myself at this time.

but with PV

@ May 10, 2013 1:49 PM in Solar Thermal is Dead

I don't care WHEN I collect it. We have net metering. I just want best yearly collection. And we are, in fact, net zero... in fact I generate more electricity than I can use (darn it!).

I am going to spend zero dollars on oil or propane or electricity. For the next 30 years. That's why I can nail down how much energy I'm using... I measure my energy usage and all my usage is electric.

The entire point I'm making is that solar thermal only looks better in the instantaneous collection efficiency numbers. In terms of yearly energy you can put into use, I think almost any residential analysis will come down solidly in favor of PV these days. Because the efficiency difference cannot erase the massive amount of time most of us spend with less load than you have collection ability, and net metering solves that issue completely.

the real question most people care about though is cost for useful energy gained. $3.50/watt installed and each watt will generate about 1.3 KWH/year here in the northeast. Add a heat pump and double some, potentially very large, percentage of those watts to apply to heating and/or allow for cooling offset. In my case it's probably about 70% of my total usage is "doubled" in this way.

So what's a regular solar thermal array sized to do more than DHW cost these days, installed, before credits?
How many useful yearly BTUs would you expect to get from it?

not that it really matters

@ May 10, 2013 12:32 PM in Solar Thermal is Dead

I don't know why you're asking that bob. I"m PV. I don't have to worry about whether I'm pitched for winter or summer... I'm pitched for yearly ideal, about 23 degrees true south.

What I'm saying is right now, at this very moment, and over the whole last month, I am absolutely cranking out solar power. I have no heating or cooling demands during this period. if I were thermal, GOBS AND GOBS of power would be utterly wasted. But my panels generate it and send it back to the grid where I can make use of my credits later, when I do have heating demands. I won't bother saying "heating and cooling" because when I have cooling I also have solar so that is offset in real time.

I don't lose anything from my tank. I have no tank to get hot and stop my collection. I don't have to have a load in real time to use my power. I can double my collection power by using heat pump technology. I can cool with my solar energy.

PV wins. Thermal is dead.

I know how much my array cost and how much it collects. Do you know how much your system would cost for someone to install, and how much energy benefit you're getting? we could settle this with math, if so.

this is still ignoring

@ May 10, 2013 9:32 AM in Solar Thermal is Dead

the fact that right now I am gobbling now massive amounts of solar energy that just isn't present in the winter.... way more than 10 or 20% more, more like double over the course of a day.... and banking it for later.

And I will use every single KWH I generate, no matter when I generate it. No "use it or lose it loss".

and I will double its effectiveness by using that KWH in a heat pump.

Solar thermal cannot compete for space heating. It can't even play the game for space cooling. That's just a fact.

mystery solved

@ April 9, 2013 10:52 AM in Grundfos alpha

we did have a zone valve in line. It has enough Cv that it shouldn't be a problem, however we have it in "manual open" mode which actually isn't open quite as much as "really open". when I bypassed the zone valve flow shot up to max.

pump is good. injection zone valves, not so much.


@ April 8, 2013 7:47 PM in Grundfos alpha

we could crank up the heat source and check for a DT for sanity. no load and no running heat source today... had a client with this issue and tested on our system and got this result...


@ April 8, 2013 7:27 PM in Grundfos alpha

we use lots of these. this is odd. I would never use autoadapt though.. hate that setting! too unpredictable.

flow meters are way over what the pump is reporting... I've got about 6 GPM just on one manifold on the flow meters here... about what I would expect. I would expect the constant pressure modes to be maxing out on their max flow and the fixed speed modes to likewise top out their curves here. 6 sets of one inch feeds with nothing but one hundred foot half inch loops on it....

we'll see if the switch does it in the morning. will report back.


@ April 8, 2013 7:13 PM in Grundfos alpha

43 watts. flow meters on every loop (but not necessarily extremely accurate ones).

we'll switch it out tomorrow and see if it's the pump... can't see where we would get 10 feet of head with 7 GPM here at all. that's barely 1 GPM per manifold...


@ April 8, 2013 6:55 PM in Grundfos alpha

yes, we've tried fixed high. with all the loops I can find twisted wide open it's topping out at 7 GPM. I have something like 45 one hundred foot loops of 1/2" pipe, in six manifolds all with 1" copper feeds. I should be double that flow... easily.

some of the loops may be airbound... 2nd floor radiant ceiling that's been shut off for quite awhile. but still. 36 solidly operating loops... and flow meter readings not agreeing with the alpha. I've seen THAT before, but the alpha was the one that was right in that case.

Grundfos alpha

@ April 8, 2013 5:34 PM in Grundfos alpha

anyone else having problems getting the alpha to display charted flow rates under conditions that should allow for it?

I have one here in my shop. when I open up my 36 one hundred foot loops, I should be able to peg the pump at max flow for each setting. Instead I can't even get it to report more than 7-8 GPM.

be curious to know if anyone else is seeing anything like that.

not really true.

@ April 8, 2013 5:32 PM in Formulas for heat-loss calculations

more PRESSURE differential more in/exfiltration. not more "convection". If you dump 500 cfm in a bedroom with no way out, you will drive exfiltration. ditto for a room with a return and no way for air to get to it.

taller buildings with stack effects is more in/exfiltration.

more holes of course = more infiltration.

radiant loads can be lower because duct losses can be lower. you might drive less infiltration but it's not inherent to the application of forced air to have higher infiltration.

zeff, your formula are correct but your inputs are still where the magic is. GIGO my friend. you have some heavy reading ahead of you on that front to get good numbers.

with chilled water

@ March 5, 2013 10:13 AM in Chilled ceiling design

flow rates must be high unless you can make really cold water. whether you tie to air or radiant this remains true.

cold water

@ March 5, 2013 9:34 AM in Chilled ceiling design

we are using a daikin altherma air to water heat pump. I am not up to speed on all the chiller options... I will say that may require super high head pumps so doing a tank with them and turning off the pump is often a great choice.


@ March 4, 2013 9:32 AM in Chilled ceiling design

in our case is a single chilled water coil in an ERV duct system... all air in is dehumidified.

has limitations if you have a leaky envelope, then you need recirc. but you don't have to dehumidify every room, as the fellow says, humidity travels pretty well.

not at all

@ January 16, 2013 10:42 AM in Misc questions on radiant

if you're cooling, I would stick with warmboard R.

if you're just heating plates and strapping work fine too. plates against the drywall.

good eye bob.

@ January 15, 2013 9:13 PM in High delta T, how to adjust it?

didn't even think about the rust.


@ January 15, 2013 9:10 PM in High delta T, how to adjust it?

there is no way the pump is undersized. I don't care how many 90's you have. if you measure it all and find that the pump is undersized, you're wrong. it's that simple.

your problem is not circ sizing. say it with me now! your problems is NOT pump sizing. it may be a bad pump, but it's not the model number causing your problem.

to get this pump down to, say, 5 GPM (where it would have to be to even run a 50 degree dt for any length of time with your boiler) you'd have to have about 10 feet of head. If your flow rate were REALLY that low, split through 2 circuits, you'd have about 1.5 feet of head in the baseboard. I don't care how many elbows you throw at it, and I don't even care what model boiler you have... you don't have 8 feet of head on top of the baseboard here at 5 GPM unless you've got something really, really weird here like a 1/2" return crossing the house or a hundred foot 3/4" combined return or something.

so this pump should be pushing significantly more flow, with a lower delta T. period. finding out why it's not is a good exercise. trying to confirm this pump is appropriate is, in all likelihood, a waste of time and energy.

but if it makes you feel better, knock yourself out.


@ January 15, 2013 6:50 PM in High delta T, how to adjust it?

tom why not? the rest of us are happy to look dumb ;)

it is true

@ January 15, 2013 6:49 PM in Misc questions on radiant

that radiant ceiling is not AS comfortable as radiant floor in heating mode. however it is also true that it is still more comfortable than baseboard or forced air of any variety.

I would put it higher than panel rads in most cases as well. though if you do have higher temperature radiators and you can stand right up on top of them, that can be nice. I like to sit very close to ragingly hot woodstoves. but for the overall comfort of the room, any full radiant surface will beat a smaller panel radiator.

I tend to avoid radiant walls because of furniture and puncture issues. I prefer ceilings for those reasons. also installation is easier.
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