Homemade Heat Pump Water Heater (R290)

[Mikesolar]

Quote from one of the UK guys who seems to know:

"Purity

The quality of commercially available propane (LPG) is very often
not suitable for refrigeration. The composition varies substantially,
generally having between 60 and 95% propane. It can have high
levels of moisture and unsaturated hydrocarbons.
Impurities such as other hydrocarbons can impact the vapour
pressure of the product, lowering overall system efficiency. Sulphur
can cause corrosion, and unsaturated hydrocarbons can react with
system components. Moisture leads to hydrolysis, corrosion and
compressor failure.

R290 is at least 97.5% pure with minimal levels of critical impurities including moisture
(typically† <10ppm), unsaturated hydrocarbons (typically <0.5%) and
sulphur. This makes it ideal for use in all types of refrigeration and air
conditioning systems."

Maybe all that is needed is to run it through a proper filter system to meet the requirements? That is something else to be checked out.

[AC_Hacker]

Originally Posted by Mikesolar

Quote from one of the UK guys who seems to know:

"Purity

The quality of commercially available propane (LPG) is very often
not suitable for refrigeration. The composition varies substantially,
generally having between 60 and 95% propane. It can have high
levels of moisture and unsaturated hydrocarbons.
Impurities such as other hydrocarbons can impact the vapour
pressure of the product, lowering overall system efficiency. Sulphur
can cause corrosion, and unsaturated hydrocarbons can react with
system components. Moisture leads to hydrolysis, corrosion and
compressor failure.

R290 is at least 97.5% pure with minimal levels of critical impurities including moisture
(typically† <10ppm), unsaturated hydrocarbons (typically <0.5%) and
sulphur. This makes it ideal for use in all types of refrigeration and air
conditioning systems."

Maybe all that is needed is to run it through a proper filter system to meet the requirements? That is something else to be checked out.

This is all true.

There is even more to it than that, the BBQ gas providers guarantee some percentage of propane, and the rest of the gas can vary, most of the rest of the gas is butane. I have read one study that addressed a butane/propane mixture and found that SOME butane can actually improve performance, particularly when the equipment is used for heating, rather than cooling.

As I recall the best % of butane was about 6% to 8%. I have asked my local supplier about the purity of propane and he said that it was 85% to 95% propane.

But if you are building the final unit (your Opus), the price of refrigeration grade propane is not all that huge, when you consider the other expenses and time invested.

Additionally, Brad_C and I think Vlad, too did some work wherein they put a tank of BBQ gas in the deep freeze and drew the gas from the top of the tank, leaving the butane at the bottom. Search the forum... lots here!


Best,

-AC

[Hv23t]

I've been working on the controls for the heat pump. More specifically I have been working on the time delay for start up of the resistance heating element. I have 2 time delay relays wired in series so I can give the heat pump up to a two hour head start before the 1000 watt element helps out. I'm also going to wire in a switch to disable the heating element altogether for summertime use. I'm expecting the recycling timer for the compressor to arrive today also, so when it does I'll wire it into this nifty enclosure I got at ace hardware.

Hv23t

[Hv23t]

Just stopped in at my parents house to say hi and check on the water heater. I think I plugged in the kill a watt on Wednesday afternoon, but I can't remember for sure. It read 5.07 kwh. So I reset it and wrote down the time so I can get an accurate time measurement. My parents havnt knowticed any difference. (havnt ran out of hot water) so that's a good sign. I will keep an eye on it now that I'm recording the info.

Hv23t

[AC_Hacker]

Originally Posted by Hv23t

Just stopped in at my parents house to say hi and check on the water heater. I think I plugged in the kill a watt on Wednesday afternoon, but I can't remember for sure. It read 5.07 kwh. So I reset it and wrote down the time so I can get an accurate time measurement. My parents havnt knowticed any difference. (havnt ran out of hot water) so that's a good sign. I will keep an eye on it now that I'm recording the info.

Hv23t

So, if I figured this on the back of a napkin...

That would be about 2 days and you've used about 5.07 Kwh in that time,
so that would be about 2.535 kwh per day. I don't know where you live, but just guessing that the rate might be maybe $0.22 per kwh, that would figure out to about $16.73 per month. I don't know how that compares to the LPG consumed... pretty much depends on your local market.

And you have some cooler weather ahead, which will make the costs go up and you'll surely do some optimizing, which would make the cost go down.

I'm really interested to see how it all pencils out over time.

Best,

-AC

[launboy]

You pay $0.22 a kwh AC? Wow, we pay $0.11, without the fees and such added in, probably $0.13 per kwh with fees and such added in.

Adam

[AC_Hacker]

Originally Posted by launboy

You pay $0.22 a kwh AC? Wow, we pay $0.11, without the fees and such added in, probably $0.13 per kwh with fees and such added in.

No no, mine's about the same as yours. I wasn't sure of your location , so I looked at several CA electric rates... Electricity is going for $0.22 (and rising) in San Francisco & Los Angeles.

But I have to say that if electricity was $0.22 per kwh, across the whole US, we'd see some serious energy conservation and some rapidly developing alternative energy going on.

Best,

-AC

[Hv23t]

Yeah .22 is way high. I think that's what my sister pays in Hawaii. She doesn't have to use the hvac much if at all. The first teir here is .12 for the first 28kwh a day in the winter and 18 in the summer. The second teir is .14 for the next 30% of the base and the third teir is .30 up to 100% of the base. I'm not sure how much power my parents use, so I'm not sure what teir the water heater is using.

Hv23t

[Hv23t]

One thing I found interesting. The propane water heater I took out was estimating the price of propane at the time (25 years ago) at .78 a gallon. The last bill I paid last January was 3.48 gallon. The primary electric water heat I installed there was about 1 year older than the propane one I took out. And it was estimating the electrical cost at .088 kwh. So over the last couple decades electricity has gone up about 37% and propane has gone up over 400%!!! I'm sure that at the time that's why my parents went propane because it was cheaper than using electric, but the tables have drastically changed.

Hv23t

[Daox]

Originally Posted by launboy

You pay $0.22 a kwh AC? Wow, we pay $0.11, without the fees and such added in, probably $0.13 per kwh with fees and such added in.

Adam

My average with fees is $0.17.