Reality of solar heat?

[peakbagger]

I find for intermittent use like heating a cold bathroom prior to and during a shower a fan forced electric heater beats an oil fired or even a baseboard heater. I just want to heat the air up not the entire mass of the room.

[J.P.M.]

If the OP is looking for something inexpensive and short term (and also DIY), weather sealing, insulation/re-insulating, and supplemental electric heat in the rooms you use is probably the most economic solution in the short term.

These oil filled radiators (i've used older models, not these) work great. They hold the heat really well and use comparatively less electric than trying to heat rooms you're not using.

https://www.amazon.com/DeLonghi-EW77...s%2C127&sr=8-4

https://www.amazon.com/PELONIS-NY150...s%2C127&sr=8-6

https://www.amazon.com/Pelonis-Porta...s%2C127&sr=8-8

They may hold heat really well and I'd sure agree that they may have some possible advantages in safety, but a 1,500 W input is still 1500 W input - and for electric resistance heat, will always lead to a 1,500 W output.

Oil transfer electric resistance heaters are no better/worse at heating a space with respect to cost than straight electric resistance heaters. Straight electric resistance or electric radiant heaters may even have a slight perceived advantage if higher temp. source heat is required for some reason(s) such as faster radiant heat transfer with perhaps some perceived warmer spot temps., but the 1,500 W input will cost the same.

If heating the same space, under the same conditions, a 1,500 W input electric heating device will run as long as any other 1,500 W electric input device regardless of what's between the conditioned space (be it oil, masonry/brick, whatever) and the electric resistance element supplying the heat. Thermal masses for the oil, masonry/brick, whatever, will slow down the response time of getting the heat to the conditioned space in some proportion to the size of the thermal mass, and large(r) size thermal mass enclosures with more surface area will keep the heating surfaces coolerand in so doing slow down the radiant heat transfer aspect of the heating process.

But under something approaching a steady state condition of heat required, the energy required to maintain a set room temp. will be the same regardless of how that energy is supplied. If the energy is supplied by electric resistance, under steady state conditions, the cost will be the same for the fuel (the electricity).

[JSchnee21]

If the OP is looking for something inexpensive and short term (and also DIY), weather sealing, insulation/re-insulating, and supplemental electric heat in the rooms you use is probably the most economic solution in the short term.

These oil filled radiators (i've used older models, not these) work great. They hold the heat really well and use comparatively less electric than trying to heat rooms you're not using.

https://www.amazon.com/DeLonghi-EW7707CM-ComforTemp-Portable-Oil-Filled/dp/B000TGDGLU/ref=sr_1_4?crid=31UWDRM8RDWTS&keywords=oil+filled+electric+radiator&qid=1576006136&sprefix=oil+filled+ele%2Caps%2C127&sr=8-4

https://www.amazon.com/PELONIS-NY1507-14A-Digital-Radiator-Control/dp/B01LEHPM7I/ref=sr_1_6?crid=31UWDRM8RDWTS&keywords=oil+filled+electric+radiator&qid=1576006136&sprefix=oil+filled+ele%2Caps%2C127&sr=8-6

https://www.amazon.com/Pelonis-Portable-Thermostat-Radiator-Protection/dp/B07TLVYXRX/ref=sr_1_8?crid=31UWDRM8RDWTS&keywords=oil+filled+electric+radiator&qid=1576006136&sprefix=oil+filled+ele%2Caps%2C127&sr=8-8

[J.P.M.]

Thank you all for your thoughtful replies.

To answer some of the questions above:

I don't have natural gas. A pipeline runs through the County and does not serve a single customer in the county.

I really doubt that there is any insulation under the basement floor.

Adding PV to heat with exceeds my space and budget.

How much time and money am I willing to expend?

Well.... With the schooling I got from all of your replies, Not enough ..... I see from your replies that solar air or water heater is not practical in my circumstance.

I suspect that if I set out to build a new house and design it to best incorporate solar heat I could probably be successful with supplemental solar heat.


I am committed to staying here for another 2-1/2 years. When I get past that I am considering building another house. I am thinking of something between 600-800sf. Hyperinsulated and built to maximize solar..

Thanks again everyone.

For anything I added that you found useful, you're most welcome.

There are many sources for retrofitting existing dwellings. W/a bit of reading and then appropriate action(s), you'll be able to get close to a min. energy design with an existing dwelling while not going broke doing so. I and others here have done so. Just start w/small projects and the low $$ stuff but read up on the what and why such conservation measures work and make sense of it before you do.

If/When you do build, or better yet, long before you build, check out passive solar, sun tempered, high mass designs. When well done and appropriately designed for the area/climate, such designs, or portions of such designs as fits your lifestyle/budget do not need to look out of place or be a full of glass monstrosity/eyesore. There's a lot of room between all and nothing in such designs. Such sun/mass tempered designs will probably cost more than a tract/stick design, but do not need to be that much more $$ if you know a bit about them. If you're willing to make some what are probably very minor lifestyle adjustments, they can be a very pleasant place to live in.

Good luck.

Add: As Bruce notes, propane is often a lot cheaper when you buy it in the summer. If you are not limited by local ordnances or the propane dealer sometimes using a larger than normal tank to get you through an entire year w/out winter buys can save a lot of $$. That might make a propane fueled scenario less costly. Propane bought around here (zip 92026) in the summer is about 30-40 % cheaper than in the winter.

[LucMan]

Here's the short answer to your question " Is there a practical solar Thermal solution to my problem" = NO. Installing PV if you have net metering available, and upgrading your heat pump to a properly sized HYperheat model would be the answer. A manual J heat loss calculation needs to be performed first so that the proper size equipment can be selected at your lowest ambient temperature with out using resistance heating. I recommend using the Mitsubishi Hyperheat (rated to -5F) model with their conventional air handler that would replace your existing AH. Duct work changes will most likely be required.
In my opinion these units exceed the performance of Geo thermal heat pumps in your climate zone. Be prepared to spend more than your quote for the wood stove.
If the above exceeds your budget then another alternative is to install a 92% propane fired furnace, propane for heating use usually is in the $2.75 per gallon range for heating use.
Just for the record with heat pumps there is no conversion of tons to BTU's as the capacity changes with the ambient temperature.

[PNW_Steve]

Thank you all for your thoughtful replies.

To answer some of the questions above:

I don't have natural gas. A pipeline runs through the County and does not serve a single customer in the county.

I really doubt that there is any insulation under the basement floor.

Adding PV to heat with exceeds my space and budget.

How much time and money am I willing to expend?

Well.... With the schooling I got from all of your replies, Not enough ..... I see from your replies that solar air or water heater is not practical in my circumstance.

I suspect that if I set out to build a new house and design it to best incorporate solar heat I could probably be successful with supplemental solar heat.


I am committed to staying here for another 2-1/2 years. When I get past that I am considering building another house. I am thinking of something between 600-800sf. Hyperinsulated and built to maximize solar..

Thanks again everyone.

[peakbagger]

I do have solar hot water on my home. Two big flat plate panels. At best I get 80 degrees over the outside ambient in winter. So on a 20 degree day I get 100 degree hot water. For the heck of it I put in some fin tube radiator on a bypass. It really does not put out much heat. Properly designed and installed radiant floor could work with those low temps and some built in radiant wall or ceiling panels also could work but for most heating systems the temp are too low to be useful.

Mechanical engineers have to take thermodynamics courses and will be familiar with exergy calculations which determines the availability of energy in system. BTUs are a measure of energy but not the availability for it to be used usefully. Folks trying to pull a fast one take advantage of this. There is a big difference between the usefulness of 1 pound of water heated to 1000 degrees F and 1000 pounds of water heated 1 degree yet the BTU content added in either mode of heating is equal. SHW has low exergy. On the other hand PV has a lower equivalent collection efficiency than SHW but with net metering the power is generated all summer and then used when needed in the winter. Depending on where you draw the boundaries the exergy is quite high of the system.With net metering the grid is effectively acting as battery as long as non renewable assets are in the loop. Unfortunately there is no current viable thermal batteries that could store energy for months like PV can be.

On an ideal sunny day with a collector perpendicular to the suns angle at best there is 1000 watts per meter of collector. Multiply by 3.412 to get btu/hr so every square meter or perfect collector may gain 3412 but/hr per meter for perfect panel. Its pretty rare to build a tracking array so the panel angle relative to the sun will change reducing its efficiency. The panels are also radiating heat back to the air while they are collecting heat. For flat panels the break even point is around an 80 degree difference between the glycol temp and the outdoor temp. This efficiency varies with the delta T across the panel. Ideally to reduce the emitter sizing in the house you want water that is considerably hotter than the house temp but that means lower collector efficiency.

If someone goes to the trouble to do the math they will rapidly come to the conclusion that its far more expensive to try to heat a home with SHW than many other options. There were a lot of failed home designs built in the 1970s and early 80s using active solar air heating. Pretty much the standard these days is super insulated design with lots of thermal mass and judicious use of glass to heat thermal mass with overhangs to reduce hot weather heating and very effective thermal shutter or insulated sealed blinds to reduce nigh time heat loss. Deep energy retrofits of existing housing can be done but they have to be done right. Its far easier to do super efficient design in new construction but few developers do it unless there are required minimum energy standards in place that are enforced. They are far better building them quick and cheap to the minimum standard and spending the savings on visual appeal items like granite counters.

[J.P.M.]

Steve:

How much do you want to lower your heating bill by and how much work, both physical and mental (learning) are you willing to put into it ?

Set your goals and remember that you probably want a comfortable living space with a lower heating bill with the lowest capital investment. Solar thermal is one tool to get there, but it's usually far down the list of measures if the list is ordered by cost effectiveness and ease of use.

Before you do anything else, know your starting point. Begin by determining what your current heat loss is, either by doing the calc/est. from a building envelope survey of each exterior surface including floors and ceiling/roofs and an est. of infiltration loss at maybe 2 air changes/hr. Or, do/get the same from an energy audit.

Then, compare those numbers to what you can measure by keeping track of what's used for heat over two 24 hour periods that both require heat but one with warmer ave. outdoor temps by ~ > 10 F. or so. That'll allow you to calc a heat loss per degree day. Multiply that degree day (DD) heat load the diff. per degree of temp. diff. by (desired indoor temp. - design (minimum) exterior temp.) to get a design heat load.

Divide that by 24 for an hourly design heat load.

Divide that by (the %age of the time the heating equipment is designed to operate) for equipment sizing. Add some excess size for the unexpected but not too much.

In comparing what you calc and what you measure, don't be surprised if the calc'd results disagree with the measured calcs by a factor of 2 or more.

That'll give you a back of the envelope est. of what you'll need to stay warm before conservation measures.

Then, start with the least expensive measures first - sealing the building envelope. Add insulation to the attic crawl space and then do the walls as best you can.

How much of your heat load is for DHW ? Get low flow shower heads and insulate the tank and lines. And, if you have one of thos B.S. hot water recirculation systems, for God's sake get rid of it.

After all that, recalc the heat loss and resize the heating plant for the new, lower load.

To your desire to know if solar thermal will work in cold climates: In sunny climates such as yours, solar thermal will probably work a lot better than in climates such as Peakbagger's or where I came from (Buffalo), but in most any case, know that until you get close to superinsulation values, your money will be much more effectively spent on measures that lower the heating requirement of the building than by adding most any solar thermal equipment to it.

Basically, conservation is a lot cheaper than solar for a lot fewer problems. That's just the way it works. I tried it for 20+ years in Buffalo. Insulation and sealing does work. Solar will work some for you, but it'll cost. I'm a big solar fan and thermal was how I started, but I lowered a energy use of an existing 1928 home by 2/3 using mostly conservation measures with about 10 % of that coming from a concerted effort at solar utilization in ways that most folks would soon tire of.

I was at a solar energy conference in the early '80's before PV was more than a distant future dream. It was a world where solar thermal ruled. Anyway, while there, I was talking to one of the solar gurus, a guy by the name of Steve Baer. He was, and I believe still is, a big solar proponent. Anyway, he said something that stuck with me and proved to be true, at least to my experience: The biggest impediment to solar energy utilization for heating a home is not the big oil or energy companies or even the solar naysayers. The biggest threat is that people will learn how much easier and more cost effective it is to insulate and reduce a building load than it is to meet a heat load with solar collectors. If/when they do figure it out, fewer active solar systems of smaller sizes will be the rule, as will passive solar for sunnier areas.

Get the heat load as low as your lifestyle permits before going beyond the simplest (probably passive) solar measures.

BTW, get new windows for aesthetics if you want them, but know that they'll have a long payback if done for energy savings only, maybe even longer than solar thermal which is close to the bottom of the list in terms of cost effectiveness and ease of use.

[bcroe]

Four tons is 48,000 BTUs.

Our heat pump is very low end. It switches to aux heat when the outside temp is around freezing. That
turns my heat pump into an electric resistance heater.

Sorry for leaving without checking, I should have said 1.5 tons is 18,000 BTU/hr, as you said 4 tons is
48,000 BTU/hr.

Our summer price for propane has been near $1/gallon. Do not buy it in mid winter, an artificially inflated
price may exceed $5. With $0.10 per KWH and 27 KWH equals the heat of a gallon of propane (burned
in a high efficiency furnace), it is cheaper to heat with electrical resistance above $2.70 a gallon.

Peakbagger and I just finished explaining how you can heat with solar, been doing it here 6 winters.
Bruce Roe

[Mike90250]

This is about the best of the DIY schemes I've seen

https://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

Also, a high efficiency pellet stove could be useful, and using an external flue outside the wall, instead of inside the house. There is even a no-electric gravity feed pellet heater

https://www.tractorsupply.com/tsc/product/us-stove-gravity-feed-non-electric-wiseway-pellet-stove-2-000-sq-ft

I am very happy with our masonry heater, but you have to build the house around it

[PNW_Steve]

The prior owner had the 1-1/2 ton unit installed. She is a widow and pretty clueless about home repairs and maintenance.

She had the local HVAC guy come out and sold her a substandard system for top dollar.

[PNW_Steve]

For cooling yes, we are discussing heating. I believe 4 tons is about 14,000 BTU/hr. My 2 furnaces
I used to use amount to some 120,000 BTU/hr. And heat pump capability tends to decrease as
winter proceeds. Bruce Roe

Four tons is 48,000 BTUs.

Our heat pump is very low end. It switches to aux heat when the outside temp is around freezing. That turns my heat pump into an electric resistance heater.

[PNW_Steve]

I assume you don't have natural gas? Is your entire house electric? Perhaps it's the region of the country, but I'm surprised a home of that vintage wouldn't have either oil, natural gas, or propane heat. Has it always been heated by heat pump? Is it a newer unit / well maintained? Or did they remove the oil tank when they flipped it?

Weather sealing and insulation are certainly the least expensive solution with the best ROI (generally). Have you had a home energy audit? A quality company that specializes in these will quickly help you find leaks, drafts, etc. Is the entire house one zone? (mine is, which sux, but I have gas fired forced hot air (which is cheap to operate) and we predominately live on the second floor -- split level.

Did you have the upgrades done, or was it flipped before you bought it? You'd be surprised what a poor job of sealing/insulating around replacement windows is commonly done. Similarly, if your 2nd floor overhangs the first by a foot or so (never understood why the do this) these ares are often poorly or not insulated at all.

PV could be a solution to offset your electric consumption, but you'd be looking at much more substantial investment -- north of $25K. Geothermal heat would be even more.

You could install supplemental baseboard heat on the first floor (electric or water). A recirculating water system would be the cheapest to operate (on natural gas, propane, or wood) but would have a much more substantial install cost. But electric baseboards are easy and cheap to install (if you can easily pull 240 feeds from a near by electrical panel).

While electric heat is generally "expensive" since you would only be heating the rooms you are in (and not trying to heat your whole house) this would likely be cheaper then running Supplemental (electric heat) on your heat pump.

A relatively new solution (in the USA) is a wood pellet boiler -- This would provide hot water for radiators and potentially replace your electric hot water heater.

https://www.maineenergysystems.com/wood-pellet-boiler/

https://www.pellergy.com/wood-pellet-boilers/

Alternatively, a high efficiency propane boiler with an inexpensive PVC Schedule 40 vent

We don't have natural gas here. There is a natural gas pipeline that runs through the county and doesn't serve a single customer in the county..

Propane is $3.25 a gallon here so it is not terribly cost effective.

Wood boilers have been around for many years. I remember seeing them advertise them seeing ads for them in MEN in the late 80's.

What I really want to know is if there an effective method of heating with solar.

[bcroe]

Given the performance of what I have now and my experience with HVAC in
houses that i have built or remodeled I think that four tons would be plenty.

For cooling yes, we are discussing heating. I believe 4 tons is about 48,000 BTU/hr. My 2 furnaces
I used to use amount to some 120,000 BTU/hr. And heat pump capability tends to decrease as
winter proceeds. Bruce Roe

[PNW_Steve]

Thermal collectors have difficulty in cold climates, because you get the least heat when you
need it most, and they do poorly or freeze up in frigid weather. Wood burning works, but
requires a constant input of time and labor to function.

I am using PV solar with net metering to solve all these problems. I have no problem keeping
the house at 75 F using mini split air to air heat pumps, for outside weather down to zero F.
When 20 below zero F and colder happen, I may need to use more of my net metering energy
reserve for some resistance heating. The propane furnace only stands by for a power outage
backup. The insulation of 5000 sq ft here is pretty poor, another project.

Your 1.5 ton heat pump is far too small for serious heating, and older designs have rather poor
efficiency. 6 tons in use here. Bruce Roe

Given the performance of what I have now and my experience with HVAC in houses that i have built or remodeled I think that four tons would be plenty.