The Homemade Heat Pump Manifesto - Page 138

AC_Hacker · 12-16-12, 08:48 AM

Quote:

Originally Posted by Mikesolar

New technology is allowing ASHP to get lower and lower in ambient temp and having a gas or electric back up can still make financial sense. It might be the choice between $40k for vertical wells and $20k for an ASHP with some solar (for example) and if the annual heating cost is less than $1000with GSHP and $1200 with ASHP, is it worth it to go GS?

Looks like you're in Canada...

I can't speak for Canada, but in the US, the average family moves about every 5 years. This means that to be attractive, an investment needs to break even before that time.

That should answer your question right there.

But otherwise, I think that there might be an error in your estimate of the difference in annual heating cost between the GSHP and ASHP. Usually ASHP have a seasonal COP of around 2.5 and GSHP have a seasonal efficiency of around 3.8. the COP ratio in that case would be close to 1 : 1.52 but your heating figure have a ratio of 1 : 1.2, over the longer term, this could make a big difference. The efficiency numbers for ASHP are very dependent on your location, and the prevailing winter conditions... GSHP installations are less dependent on local temperatures. Things happens more slowly underground.

You also neglected to include the cost of the GSHP unit and the cost of non-loopfield installation.

There is also an argument to be made about durability. By design, an ASHP will be located outside in the weather, so its service life will be much shorter, typically 10 to 15 years or so. A GSHP will be located inside, and its service life will be much longer, possibly by twice. Also, a GSHP is much less likely to be a target for vandals or thieves, who would go after the copper. (* this is a real problem. a ASHP was actually stolen from within 100 feet from my house within the last month *) Additionally, at the end of it's service life, the most expensive part of a GSHP (the loop field) will still be fully functional. I have been to GSHP installer seminars, and the stated design life of a loop field is 50 years, but everyone knows that the reality is that it will last for hundreds of years. It is just not a useful selling point to state that the loop field will last far longer than the life of the buyer or his children or their children.

So, over the short term, if your winter weather conditions are favorable, and your home-changing frequency is similar to the US average, the ASHP is a good investment.

But if you haven't checked out the DIY GSHP install done by randen, you really should. He lives in Canada, not terribly far from you, and his project has been a spectacular success.

Best,

-AC

AC_Hacker · 12-16-12, 09:05 AM

Quote:

Originally Posted by Geo NR Gee

In preparing to hack my air source heat pump, I am trying to understand the tools used for getting the correct charge. I have a Fieldpiece SMAN3 unit that hooks up to the lines and can help determine the Superheat and Subcooling...

Geo NR Gee,

It might be useful to respondents, if you posted a link to the manual for your particular field-piece.

I'm very interested in this discussion.

Best,

-AC

Geo NR Gee · 12-16-12, 11:54 AM

Quote:

Originally Posted by AC_Hacker

Geo NR Gee,

It might be useful to respondents, if you posted a link to the manual for your particular field-piece.

I'm very interested in this discussion.

Best,

-AC

Here is the link to the SMAN3 website:
Digital Manifolds - SMAN2 & SMAN3

Here is a link to the instructions:
http://fieldpiece.com/PDF/Manuals/Opman-SMAN-web.pdf

So after watching the video on the Fieldpiece website, I would use the superheat reading to dial in the charge in a fixed restrictor system and the subcooling if it is a TXV (Thermo-expansion valve) system.

Below is inside my heat pump. I see the small copper tubes and they spider leg down to what seems to me is a TXV valve. Is that right?

BradC · 12-16-12, 06:43 PM

That looks like a TXV. So yes, subcooling is the way to optimise your charge.

The theory is the higher your subcooling, the more liquid you have backing up in your condenser and the less condenser area you have for actual condensation. This raises your condensing temperature (pressure) and therefore increases your compressor work. Ideally you want as little subcooling as you can get away with to ensure a solid liquid line into the TXV. I have a sight glass in my liquid line, and I can get away with about 1.5K subcooling. Any less than that and I start to get flash gas as the liquid passes through the filter/drier.

Unfortunately the fieldpiece does not do the HC refrigerants, so you'll really want to manually calculate your subcooling from a PT chart. I bought the Testo 550 because it has both R290 and R600a. Just saves the extra effort.

Mikesolar · 12-16-12, 09:22 PM

Better price and Canadian made is the Digicool AK900 which has the p/t chart for R290. I have two of them, one for R410 and one for R22 and I might get a 3rd just for propane.

jeff5may · 12-16-12, 11:20 PM

Neo,
From the pics you took , I can see you have a TXV metered outdoor unit with a distributor feeding 9 circuits thru the heat exchanger. Due to this fact, you will not need to adjust your TXV to get good efficiency out of the unit. The pressure drop added by the distributor to equalize flow thru the 9 circuits tends to lessen the effect of adjusting the valve. In the future, you can try to squeeze a little efficiency out of the txv, but this will lessen your safety cushion in preventing flooding or starving of your compressor. With r290, flooding the compressor is much easier to do than with r22. So unless you have a suction line accumulator (I didn't see one in the pics) and want to push the envelope to gain 3-5% efficiency, just trust the factory settings for now.

A good place to start when charging with r290 is to weigh in 40% of the factory r22charge by weight. This will get you in the ballpark to fine tune your charge. Subcooling is the temp difference between the condensing temp of the gas in the hx and the actual temp of the liquid line leaving the hx. The main idea with the subcooling is more charge will tend to lower the liquid line temp. You want to adjust charge at a high ambient temp, where the difference between the gas leaving the compressor and the outdoor air is smallest and the condensing temp is high. Since it's cold, and you have to set subcooling in cooling mode, make sure your house is 75-80 degrees f before switching to cooling mode. Shut the unit off and block off airflow to the 3 large sides of your outdoor unit. Start it up in cooling mode and let it run 10 minutes or so. The outdoor unit must have at least 200 psig of head pressure to set the charge. If your head pressure is low after 10 minutes, block off more of the outdoor unit's airflow. With my window ac unit, I had to wrap the entire outdoor side of the unit with a garbage bag to get it warm enough. If it's still not high enough, make sure your indoor coil didn't freeze before adding any charge. If it did, you get to start over after it thaws back out. If not, add a little gas at a time until your head pressure rises.

Here's a PT chart for r290: HC-290 (PROPANE) PRESSURE - TEMPERATURE CHART

At 200 psig, the condensing temp for propane is 110 degrees f. Since you have a prebuilt unit, the install manual will tell you your target subcooling for your unit.. Again, trust the factory to begin with. Measure the liquid line temp and see where the subcooling temp is. If you had to add refrigerant to get the head pressure high enough in the cold weather, the subcooling will probably be higher than your target. If this is the case, you're done. It's as good as it will get in the cold weather. Revisit it on a hot summer day when mother nature isn't against you.

Onc

jeff5may · 12-16-12, 11:40 PM

Doh!

Once you reach your target subcooling, the charge of your system should not change unless it gets over 110f where you live. Again, setting total system charge is best done on the hottest day of the year in your area, when the outdoor unit is rejecting heat into the hot outdoor air. Below this max, the unit will always have more subcooling than your target. This is a good thing, since too little subcooling equals bubbles in your liquid line and a sneezing evaporator. And nobody wants to be sneezed on, especially your compressor! High performance units add in a liquid line heat exchanger to cool the liquid line to below outside temp before it gets to the TXV to further improve system gain. In theory, it takes more energy to cool liquid than to condense gas, but in a hot rod hacked unit, more heat is more heat...

In heating mode, when it is coldest outside is when to adjust the TXV. The exact opposite conditions apply: when the outdoor unit is trying to cool the air on the coldest day of the year, the TXV has to work hard to extract heat yet not starve or flood the compressor. Too much superheat, and the compressor will starve; too little superheat and the compressor will flood. With an air source unit, a few degrees of extra superheat is cheap insurance against flooding your compressor. With a water source unit, you can get much closer to the limit due to a few differences: water takes MUCH more energy to heat up than air, and with a ground source your loop temps don't swing anywhere near what the outdoor air does.

Mikesolar · 12-17-12, 05:41 AM

Quote:

Originally Posted by AC_Hacker

Looks like you're in Canada...

I can't speak for Canada, but in the US, the average family moves about every 5 years. This means that to be attractive, an investment needs to break even before that time.

That should answer your question right there.

But otherwise, I think that there might be an error in your estimate of the difference in annual heating cost between the GSHP and ASHP. Usually ASHP have a seasonal COP of around 2.5 and GSHP have a seasonal efficiency of around 3.8. the COP ratio in that case would be close to 1 : 1.52 but your heating figure have a ratio of 1 : 1.2, over the longer term, this could make a big difference. The efficiency numbers for ASHP are very dependent on your location, and the prevailing winter conditions... GSHP installations are less dependent on local temperatures. Things happens more slowly underground.

You also neglected to include the cost of the GSHP unit and the cost of non-loopfield installation.

There is also an argument to be made about durability. By design, an ASHP will be located outside in the weather, so its service life will be much shorter, typically 10 to 15 years or so. A GSHP will be located inside, and its service life will be much longer, possibly by twice. Also, a GSHP is much less likely to be a target for vandals or thieves, who would go after the copper. (* this is a real problem. a ASHP was actually stolen from within 100 feet from my house within the last month *) Additionally, at the end of it's service life, the most expensive part of a GSHP (the loop field) will still be fully functional. I have been to GSHP installer seminars, and the stated design life of a loop field is 50 years, but everyone knows that the reality is that it will last for hundreds of years. It is just not a useful selling point to state that the loop field will last far longer than the life of the buyer or his children or their children.

So, over the short term, if your winter weather conditions are favorable, and your home-changing frequency is similar to the US average, the ASHP is a good investment.

But if you haven't checked out the DIY GSHP install done by randen, you really should. He lives in Canada, not terribly far from you, and his project has been a spectacular success.

Best,

-AC

Actually, the ASHPs I refer to are not the Fujitsu and Mitsi of the world but ones that will heat water for floor heating with an air top up (if needed) and are indoors like a GSHP. Randon has done the floor heat system (which I have seen) and I am in the sloooooww process of doing it too. The ASHPs my mentor makes have COPs of around 5 because he uses waste heat from different sources and really watches his pumping power so I know it can be done. The problem with his system is that it cannot be a package unit because it is built for the situation. He has one residential ASHP that has been in for 30 years and we just replaced a defrost timer. Other than maintenance, nothing else has been done.

The numbers I stated were approximate and I agree that ASHPs are way more local weather dependent but I dis-agree about the short payback issue. If you tell most people there is a GSHP in the house, the resale cost of the house increases and people know they will get their money back. I have no proof of this but I think that most people who go to the length of putting GSHPs in, think longer term and want to stay a long while.

I haven't heard of theft problems in our area for AC units but I have heard of it in the USA and seen strange ugly cages being built around some systems. Weird.

About R290, I have been warned a few times that the HP needs to be placed outdoors for safety reasons and I am debating doing this at my house partly because there is a bsmt bedroom next to the mechanical room so there will be some noise issues. I always wanted to keep it indoors so I didn't have to use the crankcase heater.

BradC · 12-17-12, 07:30 AM

Quote:

Originally Posted by Mikesolar

About R290, I have been warned a few times that the HP needs to be placed outdoors for safety reasons and I am debating doing this at my house partly because there is a bsmt bedroom next to the mechanical room so there will be some noise issues. I always wanted to keep it indoors so I didn't have to use the crankcase heater.

On my cooling only system I've got around the need for the crank case heater by using a liquid line pumpdown solenoid. In my case I did it because I don't want the in-roof units left with ready access to 3 or 4 litres of liquid propane, so when it pumps down everything is contained in the condenser and the remote units are left with about 60 psi of gas. I then monitor that using the low side pressure sensor to check for leakage (gas or liquid).

I do know however that this is a much more awkward proposition if you have a reversing valve in the circuit.

randen · 12-17-12, 08:38 AM

Mikesolar

I had a thought concerning the indoor R290 leakage fear. What about a very small bilge air pump (fan) to remove air from the HP housing much like that used in the boating industry that remove gasoline vapours from the engine compartment. The direct vent on natural gas fired water heaters etc use this to assure CO is moved out of the house, so for piece of mind a small one on the HP compressor enclosure could be employed. A small squirl cage fan operated at a slow speed to extend its life with some sort of simple sensing to confirm its operation.

I would agree that a leak in a small basement from our R290 GSHP's may have the potential for a bad day but I'm of mind that many basements have an unlimited supply of natural gas entering and I would think some would have slow leaks going un-noticed. Remember that the air/fuel mix has to be perfect for the spectacular event. Many refrig. units operate for their entire lives with their original charge gas. I sleep well having weighing out these thoughts and I had been diligent to make good brazed connections on my DIY GSHP.

Randen

12-16-12, 11:40 PM	#1377
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 432 Thanked 619 Times in 517 Posts	Doh! Once you reach your target subcooling, the charge of your system should not change unless it gets over 110f where you live. Again, setting total system charge is best done on the hottest day of the year in your area, when the outdoor unit is rejecting heat into the hot outdoor air. Below this max, the unit will always have more subcooling than your target. This is a good thing, since too little subcooling equals bubbles in your liquid line and a sneezing evaporator. And nobody wants to be sneezed on, especially your compressor! High performance units add in a liquid line heat exchanger to cool the liquid line to below outside temp before it gets to the TXV to further improve system gain. In theory, it takes more energy to cool liquid than to condense gas, but in a hot rod hacked unit, more heat is more heat... In heating mode, when it is coldest outside is when to adjust the TXV. The exact opposite conditions apply: when the outdoor unit is trying to cool the air on the coldest day of the year, the TXV has to work hard to extract heat yet not starve or flood the compressor. Too much superheat, and the compressor will starve; too little superheat and the compressor will flood. With an air source unit, a few degrees of extra superheat is cheap insurance against flooding your compressor. With a water source unit, you can get much closer to the limit due to a few differences: water takes MUCH more energy to heat up than air, and with a ground source your loop temps don't swing anywhere near what the outdoor air does. Last edited by jeff5may; 12-17-12 at 12:02 AM..

12-16-12, 06:43 PM	#1374
BradC Apprentice EcoRenovator Join Date: Dec 2010 Location: Western Australia Posts: 148 Thanks: 1 Thanked 48 Times in 34 Posts	That looks like a TXV. So yes, subcooling is the way to optimise your charge. The theory is the higher your subcooling, the more liquid you have backing up in your condenser and the less condenser area you have for actual condensation. This raises your condensing temperature (pressure) and therefore increases your compressor work. Ideally you want as little subcooling as you can get away with to ensure a solid liquid line into the TXV. I have a sight glass in my liquid line, and I can get away with about 1.5K subcooling. Any less than that and I start to get flash gas as the liquid passes through the filter/drier. Unfortunately the fieldpiece does not do the HC refrigerants, so you'll really want to manually calculate your subcooling from a PT chart. I bought the Testo 550 because it has both R290 and R600a. Just saves the extra effort.

12-16-12, 09:22 PM	#1375
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	Better price and Canadian made is the Digicool AK900 which has the p/t chart for R290. I have two of them, one for R410 and one for R22 and I might get a 3rd just for propane.

12-16-12, 11:20 PM	#1376
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 432 Thanked 619 Times in 517 Posts	Neo, From the pics you took , I can see you have a TXV metered outdoor unit with a distributor feeding 9 circuits thru the heat exchanger. Due to this fact, you will not need to adjust your TXV to get good efficiency out of the unit. The pressure drop added by the distributor to equalize flow thru the 9 circuits tends to lessen the effect of adjusting the valve. In the future, you can try to squeeze a little efficiency out of the txv, but this will lessen your safety cushion in preventing flooding or starving of your compressor. With r290, flooding the compressor is much easier to do than with r22. So unless you have a suction line accumulator (I didn't see one in the pics) and want to push the envelope to gain 3-5% efficiency, just trust the factory settings for now. A good place to start when charging with r290 is to weigh in 40% of the factory r22charge by weight. This will get you in the ballpark to fine tune your charge. Subcooling is the temp difference between the condensing temp of the gas in the hx and the actual temp of the liquid line leaving the hx. The main idea with the subcooling is more charge will tend to lower the liquid line temp. You want to adjust charge at a high ambient temp, where the difference between the gas leaving the compressor and the outdoor air is smallest and the condensing temp is high. Since it's cold, and you have to set subcooling in cooling mode, make sure your house is 75-80 degrees f before switching to cooling mode. Shut the unit off and block off airflow to the 3 large sides of your outdoor unit. Start it up in cooling mode and let it run 10 minutes or so. The outdoor unit must have at least 200 psig of head pressure to set the charge. If your head pressure is low after 10 minutes, block off more of the outdoor unit's airflow. With my window ac unit, I had to wrap the entire outdoor side of the unit with a garbage bag to get it warm enough. If it's still not high enough, make sure your indoor coil didn't freeze before adding any charge. If it did, you get to start over after it thaws back out. If not, add a little gas at a time until your head pressure rises. Here's a PT chart for r290: HC-290 (PROPANE) PRESSURE - TEMPERATURE CHART At 200 psig, the condensing temp for propane is 110 degrees f. Since you have a prebuilt unit, the install manual will tell you your target subcooling for your unit.. Again, trust the factory to begin with. Measure the liquid line temp and see where the subcooling temp is. If you had to add refrigerant to get the head pressure high enough in the cold weather, the subcooling will probably be higher than your target. If this is the case, you're done. It's as good as it will get in the cold weather. Revisit it on a hot summer day when mother nature isn't against you. Onc

12-17-12, 08:38 AM	#1380
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 658 Thanks: 9 Thanked 193 Times in 131 Posts	Mikesolar I had a thought concerning the indoor R290 leakage fear. What about a very small bilge air pump (fan) to remove air from the HP housing much like that used in the boating industry that remove gasoline vapours from the engine compartment. The direct vent on natural gas fired water heaters etc use this to assure CO is moved out of the house, so for piece of mind a small one on the HP compressor enclosure could be employed. A small squirl cage fan operated at a slow speed to extend its life with some sort of simple sensing to confirm its operation. I would agree that a leak in a small basement from our R290 GSHP's may have the potential for a bad day but I'm of mind that many basements have an unlimited supply of natural gas entering and I would think some would have slow leaks going un-noticed. Remember that the air/fuel mix has to be perfect for the spectacular event. Many refrig. units operate for their entire lives with their original charge gas. I sleep well having weighing out these thoughts and I had been diligent to make good brazed connections on my DIY GSHP. Randen