The Homemade Heat Pump Manifesto

[S-F]

I just have to chime in here. This is pretty incredible AC Hacker. I wish you the best of luck with it and I look forward eagerly to see how this all pans out.

That being said, after I first read this thread (took me the better part of a morning) I started to poke around here and get some feedback from people who have geothermal systems. The responses seem to be about 2/3 dissatisfaction and 1/3 praise. The happy people are all really in to the technology and mostly had electric or oil heat before. The rest all had gas and are now quite upset that they are getting $300 electric bills a month. One person told me that on several occasions their foundation has frozen straight down to the footing. More than 2/3 of them complain about how persnickety the heat pumps are and how they can't change the temperature without the aux heat kicking in. One person said that during their first winter with it they turned their heat down during the day and up again in the evening and so on. Their electricity bill was over $600 a month which was more than their previous electric heating cost. Maybe the loops are all a little too small or something like that. All of this has made me decide to go with natural gas for my new construction and concentrate more on insulation. If I can get the house to the point where I can heat it with farts the heat generated by my highly active children I shouldn't need to worry about digging wells and fiddling with heat pumps.

Sorry to be a negative Nancy.

This thread is pretty exciting. I'm watching with rapt attention.

[Geo NR Gee]

When I had an air heat pump, if you turned up the heat, the heat strip would come on. Yes the bill went up, but not by much.

But like you and others say, insulate, insulate, insulate.

[Xringer]

S-F, if you think a GSHP isn't for you, maybe you should check out the ASHP..
If you don't live too far north, a mini-split (inverter type) might be a good investment,
to hold you over, until you can get your new build done..

Here's mine:
http://ecorenovator.org/forum/geothe...l-project.html
Cost peanuts to run, compared to oil or direct electric space heat..

A few people have posted about their DIY installs, and I expect to see some
operating $ numbers posted by spring time.



The snow this winter is pretty high. Up to the meter.
I turn off the Sanyo if it's heavy or blowing snow, (to avoid defrost cycles),
and when it gets down below 10deg F.
But, tonight, it's only going down to 12deg F, so we won't be using
any heating oil tonight.

The Sanyo will use about 500w all night long. Way cheaper than oil..
Last week, it burned about 9 kWh a day. About $1.80 a day.(21 cents/kWh)
Heating oil is over $3 a gallon now.

And, if your power co. charges too much? How about adding some PV??

[S-F]

Well I'm in MA too. Out in Northampton. I have read your minisplit thread and continue to follow it closely. It's quite inspirational. Whatever I end up with it's going to be forced hot air. Once the rest of the construction is done I can asses my budget and then decide what route to take. If I do go ASHP I also have to install a conventional furnace because when the temperature gets down to around 0 and ASHP will only operate at 100% efficiency. A gas furnace with 96% efficiency is still less efficient but will cost a LOT less to operate.

[Xringer]

What size house do you plan to build? Because, if it's small enough, the back-up heat
for a mini-split can just be plain old electrical heating elements, or a small solid fuel stove.

If oil gets much higher, I will consider solid fuel again. But, for weather like this..
(A mild 22.3F and sunny) A small tight house with a mini-split can be heat cheaply.
Mine cost is about $2 a day right now, and that's with a LOT of air leaks.

~~~

My Den has loads of glass. Not to hard to cool in summer, but heating it?
Just about doubles my cost. I've been keeping one of those oil-filled space
heaters in there, just to keep the baseboard pipe from freezing..
I've been keeping it at 50F at night.

BUT, That's about to end..

Easy Heat wires, only come on when they are needed to prevent freezing!
It's kinda like one of those Gutter-melt wires, but automatic..


Speaking of gutter wires, I've been thinking about the ice that forms
on the Sanyo coil during snow storms.. I wonder if there is an application there.?.

[Piwoslaw]

In my little booklet on heat pumps I found this picture of what not to do:

Here is a translation of the caption:

With all these construction errors that can be seen, it's hard to believe that this homemade heat pump actually works. The diameter of the plumbing on the ground source side (left) is too small, and the circulation pump too weak, which suggests that not enough heat is being supplied to the compressor. Since a working heat pump always draws the same amount of heat (this depends on its technical specifications), then with the GS side undersized the compressor started to draw heat from its surroundings, causing it to become covered with ice. The builder of this heat pump, not knowing the real reason of the icing, in an act of desperation insulated the whole case with polyurethane foam.

[AC_Hacker]

Originally Posted by Jazzoo

In related material to/from the "German" site(s) you've previously posted, looks like there are "custom" blends used in some applications (here I'm thinking of the paper "Building and alcohol trap." As pascal indicates "pressure is pressure."

Yeah, the use of blended refrigerants looks pretty interesting. I read a bio of the guy who is doing this work, and his 'street creds' are pretty darn high quality.

I would recommend readers of this thread that they consider experimenting with blended refrigerants only after they have successfully built and run their own systems, and have determined that refrigerant blending is required to achieve a particular goal. I think that the learning curve will be steep enough and should be undertaken in small successes.

For example, I have a friend who is very smart and good-hearted, but I have observed that many of the projects he undertakes get so complexified that they seldom work and he has ended up building a large reservoir of frustration rather than a large reservoir of skills.

Originally Posted by Jazzoo

One thing I forgot to mention, several models had TXOs. Hummmm, wonder if we could re-purpose these...

TXOs, what are they?

Originally Posted by Jazzoo

No, however; I have done some limited business with Paul and can verify he is a stand-up guy. As far as development environments, this really comes down to what you prefer or have become accustomed to using. The Teensy /(++) looks like a nice solution to prototyping if you do not have the skills or time to fab your own board. With exception to their respective combination of bells and whistles; every AVR is exactly like ever-other AVR. If you work with one AVR you have worked with all AVRs. Generally they all use the same SPI header to "program (read flash)" the chip. The devil lives in the included devices (on board) take a look at the Errata sheet(s) for a fair look at the "got-chas" your chip may hold.

Regardless of the family of chip you choose to work with (AVR, MSP430, Blackfin, Atom, Geo, etc.); your starting point should be...

I'm sure that any of these chips will work. My favorite would be an Arduino or some Arduino clone, just because they have such a large following, and such a large code base to take advantage of. There is also a better chance that there will be an Arduino support group in just about anybodies community. Often this can mean the difference between success and failure.

I suggested the Teensy because it's cheap and with a minor tweak can use the Arduino development scheme.

I'd like to keep everything as cheap and simple and as easy for readers to replicate successfully as possible.

I could send you a Teensy if you need...

Regarding soft starts & soft stops:

Originally Posted by Jazzoo

PWM (Pulse Width Modulation) driver for the circulation pump(s). PWM would give you the ability to implement both "soft-stops" and "soft-starts". IMHO mechanical things HATE sudden change. Mass likes to start moving slowly then accelerate through a smooth curve, logarithmically. The converse is also true. On start-up we increase the "duty-cycle" until we reach the operating voltage of the loop pump. On shut-down, we walk the "duty-cycle" down until we reach 0. Most controllers implement PWM so most of the hard work has already been done. I use this for fan speed, augar, and loop pump control on my outside wood furnace.

OK... I'm pretty sure that most off-the-shelf circulation pumps are going to use AC shaded pole or induction motors. I do know of a few that use DC motors, but the choices are smaller and the prices might be higher. Do you know or have you actually tried to use PWM technique on the AC kinds of motors?

Regarding 'warmer clime'...

Originally Posted by Jazzoo

Man, do you need someone to carry your bags?

Thanks for the offer, but I packed pretty light.

Here's a pic of the kind of boat my friend had:

Way more than I could ever afford, but what a nice experience!

* * *

But now I'm back and motivated to keep the Homemade Heat Pump Manifesto moving forward.

Regards,

-AC_Hacker

[AC_Hacker]

Hi morphector,

Originally Posted by morphector

I tough a bit after reading a bit all pages of this thread.

You could easily add a big tank of water to get some storage so when it's really cold you're not using any back-up heater.

This is a good idea. It is very common to use water or concrete for short-term storage to keep the compressor from coming on too often. When the storage is used for short term like this it is referred to as a 'buffer'. When a 80 gallon (or so) tank of water is used this way it's referred to as a buffer tank. The heat is withdrawn from the tank perhaps several times per hour, to once every few hours, depending on heating requirements.

And if you really think about it, a GSHP system is using the earth for heat storage, but it is very long term heat storage, the heat is deposited maybe just by the sun during the warmer months, or if you are using a GSHP for cooling, by the sun AND you are storing heat that is extracted from your house during the summer, too.

But If I understand you, you are thinking about using a tank for medium-term heat storage. Water is a good choice because it is cheap and environmentally safe.

I'll simplify things a bit by assuming that the tank will not lose any heat and see if I decided to use something like this on my house, how it might work out. [You could do a similar analysis if you know what your design temp is, what your heat load is, how big your heat pump would have to be to do the job, etc, etc...]

1000 gallons of water would weigh 8350 pounds.

The hottest I might be able to heat the water up would be about 180F degrees. I'm choosing this number because most of the plastic piping and tank materials I'm familiar with will begin to soften above 180F. I also have to figure that my heat pump looses efficiency as it has to elevate temperature more, so I'll set my upper limit to 110F, and see what that looks like. [note that if you are considering central air, your heat pump will have to raise the water temps to 120F or higher]

The coldest I could go on the tank would be 32F because that's when ice forms, and liquid flow stops. I think a three degree margin of safety would be smart, so I'll say that my minimum temperature would be 35F.

If I were to consider the heat that could be stored in one pound of water over that heat range, I would multiply the heat range times the amount of water.

BTU = (T1 - T2) * W

BTU = (110 - 35) * 1

BTU = 75 BTU

But since I have 8350 pounds of water,

BTU = (T1 - T2) * W

BTU = (110 - 35) * 8350

BTU = 626,250 BTU

My house is small, at 700 sq ft, and it is well insulated, and the temperatures where I live are pretty moderate. Also, I have adopted the strategy that when temperatures plunge down to the low numbers, I start closing off parts of the house I don't absolutely need to heat. So I have learned that I can actually get by with 3/4 Ton (9,000 BTU/hr) of heating.

I have observed that on warmer spring and fall days, I don't need any extra heat at all when the outside temp is 55F or higher. So this would be the equilibrium temperature.

Around here where I live, the 'design temperature' for heat pump systems is 17F. In other words, my heat pump should be able to heat my house (for me, the part that I choose to heat) to 66F without any axillary power. I can expect that in any year there will be less than a week of days at this temperature. I do know that in a year we may get one or two days at temps LOWER than 17F, for instance, earlier this year it hit 12 for about 12 hours. I turned on the kitchen stove oven for this and used a resistance heater a bit. In thirty five years I have seen it go as low as 5F only once.

So, I'll use 66F as my balance point, and 17F as my design temp. The average between those temps is 41.5F which, interestingly, is pretty darn close to the average temperature here in the winter (statistical average Dec & Jan temp is 39.5F). Since I turn the heat off at night, I'll go with 41.5F as my average temperature.

The new heat pump that is now sitting in parts on my work bench, that am building should be able to give me 7,800 BTU/hour. Not so much by average American standards, but since I'm not an average American, it should do OK.

I'm going to make a simplifying assumption that if it takes 9,000 BTU/hr to keep my house warm on a 'design day' (17F) then it should take 4,500 BTU/hr to keep it warm on an average day. This is actually a bit of an over-estimate, as I have monitored my power consumption of my mini-split to be somewhat less than that, but I'll stick with the 4500 BTU/hr for simplicity...

So on an average day, my heat pump will produce heat for my house and still have a bit of margin of excess power that could be used to slowly bring the 1000 gallon tank up to temperature, but I will disregard that. At night when the power is cheaper and I don't need to heat my house, I could use use all or nearly all of the duty cycle to warm the tank.

To bring the tank from 43F (my typical unheated basement temperature in winter) to 110F would require 107 BTU per pound or 107 * 8350 = 893,450 total. If I assumed that night was 8 hours long and I was running a 100% duty cycle, I would produce 8 * 7,800 BTU/night or 62400 BTU/night.

So it would take me 893450 BTU divided by 62400 BTU/night = 14.3 nights or just over two weeks to bring it up to temperature.

So, now let's look at what that would do for me during the 'design days'...

During the design days, I would require 9,000 BTU/hr during the 16 hours I heat my house. This would be a daily heat load of 144000 BTUs. Since I could replenish 62400 BTU at night, my net daily heat load would be 144000 - 62400 = 81600 BTU/day.

So running only off of the heat storage tank during the day, and replenishing during the night, I could endure 626,250 BTU / 81600 BTU/day = 7.5 'design days'.

For my small house, that would work just great and I could get by quite nicely. But getting back to your question, when the oitside temps go lower than design temp, the heat in the tank would be used up more quickly.

Some improvements to this system might be the addition of a solar panel or two to help heat the tank on our rare sunny days. Where I live, the winter time is mostly overcast. But when it gets really cold, we lose our cloud cover and the sun usually breaks through, so that could really help.

BTW, here's a link to a technical illustration of a 1000 gallon tank.

It looks like 1000 gallon tanks cost about $600, shipping extra.

Originally Posted by morphector

I really like the way your condenser is set-up, would there be a lot of losses by running glycol in a radiator outside instead of having real condenser outside?

The condenser is the part of the heat pump that gets hot and is inside when the heat pump is used for heating. But otherwise, glycol usually reduces efficiency by about 15%.

Hope this helps.

Regards,

-AC_Hacker

[AC_Hacker]

Originally Posted by Piwoslaw

In my little booklet on heat pumps I found this picture of what not to do...

Yes, the system does need to be balanced.

But out of curiosity, does your little booklet also have pictures of how a homemade heat pump should be built, or is the picture that is in the booklet meant to discourage all readers from building their own?

I have noticed that HVAC folks that are 'in the trade' treat real DIY people very poorly.

If the word got out that it is possible to make your own heat pump, some of those HVAC folks could be looking for another job.

-AC_Hacker

[Drake]

When researching high temp water heat storage and low temp radiant floor heating I wasn't sure how they could work together but came across in IPEX manual how a 3-way mixer can be used to return cooled loop water to new hot water to lower temp to "low heat" levels. So one can, in theory store, heated water up to near boiling and still use it. Pressure safety and high heat capable plumbing needed to mixer of course. I realize high temps are difficult for HPs but I want small wood fire aux/backup in my radiant heat system because it is free and our rural elec is not fully reliable. This can reach high temp readily. Wonder where the point of diminishing return is for trying to store heat in water? Would there be any advantage to more than "buffer" storage with a HP? It is pretty much an on-demand heat source isn't it? Unlike solar or "off peak elec". There seems to be so many options for levels/ types of heat demand it is mind boggling and surely not just one way for everyone to accomplish it. The theories seem easy the details are harder.