The Homemade Heat Pump Manifesto - Page 146

AC_Hacker · 03-29-13, 06:13 PM

Quote:

Originally Posted by Ormston

...i may not have chosen the best AC as a first heat pump...

Did you ever say what it was that you were going to do with this unit?

-AC

michael · 03-30-13, 01:44 AM

I've begun collecting data from my little E-Tech 1-ton water-to-water heat pump (originally mentioned in another thread; photo below as a reminder). The source water comes into the device at 57 degrees and exits at about 48. I can increase the difference by throttling down the water flow somewhat, but it requires no less than 2 gpm, and that's about where it stands with a difference of 10 degrees. The heated water comes out about ten degrees hotter than when it enters the heat exchanger, and if I reduce that flow, I can get a 15 degree difference, but that's it. Clearly this heat pump cannot be connected directly to a radiant floor but will require a sizable buffer tank first to allow it to get the water temperature high enough to warm a floor, and second, to build up a cushion of stored heat for periods of high demand. I'm beginning to grasp how important it is to size a heat pump carefully to the size and heat rentention rate of a particular house.

This particular heat pump was built to be a water heater either with an indirectly fired water tank or with an electric or gas tank that had been converted, and it would still be a good candidate for that.

A little studying has convinced me that heating DHW, at least for my family, is the absolute least of our heating worries, and pales by comparison to heating the house. Because we are in a controlled water district even though we have our own well, we monitor and report our water use every month. We use an average of 60 gallons of water per day for all domestic use, i.e. drinking, cooking, washing, bathing, etc. Of that 60 gallons, only a portion is heated, and I would estimate that at 20 gallons a day. That would consume about 1/10 gallon of diesel in our water heater with an annual cost of less than $150. I'd be happy to save some of that $, but it's clear to me that going to extreme measures to reduce DHW heating cost is putting effort in the wrong place. Got to get house heat, which is more than ten times the cost of DHW, under control, and that's why I'm chasing after the idea of a GSHP.

cbearden · 03-30-13, 05:15 AM

AC, Michael,
I noticed in his pic that the copper water exchanger in the back looks like the water wouldn't have enough length to exchange more heat to gain more efficiency out of the water heating that Michael is speaking of.
Would a heat exchanger similar to what you've used be more efficient for what he's doing?

michael · 03-30-13, 03:38 PM

Thank you all once again for this long, rich thread; it has become my main inspiration for continuing to work on heat pump system design. I continue to struggle with knowing how to size the heat pump and how to design and size the source pipe array, but every day I read folk's posts brings me closer to a solution.

In addition to the heat pump system per se, I'm working on a heat sequestration idea which I suspect is not novel, but holds some promise for my situation. Our house has a large attic that collects a great deal of heat on even overcast days. I propose to collect that heat and store it in the same ground field that the heat pump will use for its source.

I've conducted some crude experiments, illustrated below in photographs, and I can obtain more than half the heat I need for our house from the attic space, but the difficulty has always been that, in general, we don't need the heat during the day when it's available. One 80 or 120 gallon tank of hot water can be collected pretty quickly, but it won't be nearly enough to keep the house warm through the evening and night. In another post I have referenced collecting data on soil temperature and heat movement in soil. I have discovered that heat moves quite slowly through the soil. I could circulate 60 to 110 degree water from the attic to the soil in the location of the source pipes, and heat absorbed by the soil from the source piping won't dissipate far from the pipe in the few hours until it is needed in the evening when the attic circulation system would shut down and heat pump system would start up. In this manner I could recharge the soil heat bank any time the temperature in our attic rose to above 55 degrees

The photos below show two attempts to salvage heat from the attic, and they proved equally effective. I circulated water during warm periods and collected the heat in a 55 gallon drum in order to measure potential BTU/h gain from the attic, and I felt the results were heartening enough to merit development.

System one utilizes slinky type coils held off the roof sheathing enough so that re-roofing wouldn’t endanger the coils. The coils were connected in series and covered with reflective mylar backed by 1” styrofoam. There is lots of space for such heat exchangers, but I installed only four panels for the experiment.

System two utilizes a fan coil and crude duct work that draws air from the attic peak and blows the cooled air down toward the floor of the attic. One small fan coil collected as much heat in a given time period as did the four coils of polybutylene, and it seems a much simpler solution. It also has the advantage of avoiding trapping heat next to the roof sheathing.

As long as the attic air temp remains above the soil temp near the source pips, heat can be sequestered in the soil until needed. It seems to be the case that nearly all the heat near the surface of the earth, say within the first few hundred feet, comes from solar radiation, and only a small amount comes from geothermal heat migrating to the surface. By sequestering heat from my attic in the ground, I’d only be boosting the normal activity of the sun and providing easy access for removal via the heat pump.

Mikesolar · 03-30-13, 04:00 PM

I would pump the water down to a 120gal hot water tank (or as big as you can get) and then pump that water to the HP at night through a 3 way valve to limit the water temp from going higher than say....60F. That roof could be a big solar collector if you want it to be. The other benefit is that the ground will have more time to regenerate naturally. I am not a big fan of underground storage unless it is designed right. (look up Okatokes, Alberta solar geo system). When the tank comes down in temp to the ground temp, switch over with a diverting valve. Some people have tried to do single home systems dumping the heat directly into the ground near the piping but other then a good heat dump, it wasn't overly effective. Dumping the heat into the liquid was more so.

AC_Hacker · 03-30-13, 08:33 PM

Quote:

Originally Posted by michael

...The source water comes into the device at 57 degrees and exits at about 48. I can increase the difference by throttling down the water flow somewhat...

I have nearly gotten into fistfights over this one, BUT...

When you reduce the water flow, it is true that you will allow the temperature to go higher in the water that comes out, because you have increased the dwell time. However (this is where the fistfight begins) by decreasing the flow, you will reduce the total heat output per unit of time.

At the same time, increasing the flow rate through a pipe will increase the power required exponentially... to be exact, to double the velocity through the same pipe pipe, will require you to quadrupal the power required, due to fluid friction.

So, there is a 'sweet spot' where power required is balanced by heat rate obtained.

Quote:

Originally Posted by michael

Clearly this heat pump cannot be connected directly to a radiant floor...

This will actually depend on the mass of your floor. Your floor might have enough mass, as installed, to balance the heat pump. If not, a buffer tank would be required to add more thermal mass to the floor system. The buffer tank is smaller and is intended to hold enough heat to smooth out the on-off cycling of the heat pump. This could be compared to a capacitor in an electric curcuit.

Quote:

Originally Posted by michael

...to build up a cushion of stored heat for periods of high demand.

The water tank can serve this function, but your language suggests that now you are interested in using the tank not as a buffer tank, but as hot water heat storage. Now, you are using your water tank as a storage battery.

Quote:

Originally Posted by michael

...I'm beginning to grasp how important it is to size a heat pump carefully to the size and heat retention rate of a particular house.

Awesome!

Quote:

Originally Posted by michael

This particular heat pump was built to be a water heater either with an indirectly fired water tank or with an electric or gas tank that had been converted, and it would still be a good candidate for that.

I sure wouldn't give it away!

Quote:

Originally Posted by michael

A little studying has convinced me that heating DHW, at least for my family, is the absolute least of our heating worries, and pales by comparison to heating the house. Because we are in a controlled water district even though we have our own well, we monitor and report our water use every month. We use an average of 60 gallons of water per day for all domestic use, i.e. drinking, cooking, washing, bathing, etc. Of that 60 gallons, only a portion is heated, and I would estimate that at 20 gallons a day. That would consume about 1/10 gallon of diesel in our water heater with an annual cost of less than $150. I'd be happy to save some of that $, but it's clear to me that going to extreme measures to reduce DHW heating cost is putting effort in the wrong place. Got to get house heat, which is more than ten times the cost of DHW, under control, and that's why I'm chasing after the idea of a GSHP.

Great insights here.

Do you know if there are any local restrictions on 'Pump & Dump'? In other words withdrawing water from a well, extracting the heat, and then returning the water?

Best,

-AC

AC_Hacker · 03-30-13, 08:42 PM

Quote:

Originally Posted by cbearden

AC, Michael,
I noticed in his pic that the copper water exchanger in the back looks like the water wouldn't have enough length to exchange more heat to gain more efficiency out of the water heating that Michael is speaking of.
Would a heat exchanger similar to what you've used be more efficient for what he's doing?

The brazed plate HXs are pretty amazing. Because of the way they're constructed, with the plates being so close together, and all surfaces being involved in the heat exchange, they are incredibly efficient for their size. But, yes, a longer brazed plate would be more favorable.

BUT, brazed plate HXs are not a good idea for open source, because the plates, being so close, easily suffer from particulate deposit, thus reducing the flow rate through the space between the plates. So if you were only circulating water through a hydronic slab, brazed plate would be appropriate. If you are using an open water source, like well water, as a source, brazed plate could easily become problematic. That is why Brad_C has been very careful to filter the water that is coming into his Ground Source Air Conditioner.

-AC

michael · 03-31-13, 12:33 AM

Hello AC, You won't be getting into any fist fight with me! I couldn't agree more, if for no other reason than that the designers of the heat pump had the balance you speak of in mind when they sized the heat exchanger and the circulating pump. And I think we're in agreement on the second comment as well. When I wrote "cushion of stored heat...demand," I pictured higher demand causing a kind of rapid cycling of the heat pump that would be smoothed out if it could operate on a larger mass of water. I'm using the "pump and dump" concept here while I'm checking out the operation of the heat pump, but that's only because I don't have a closed source of water for heat, and I'm pumping and dumping from a 5000 gallon water storage tank, not between wells. I can't give a definitive answer to the question about local restrictions, but my gut tells me what with how touchy everyone is about water here, there'd be a lifetime of hoops to go through. Another reason it may not be a workable idea here is the sheer quantity of water required. One of our wells produces 75 gallons a day, and the other about 100 per day. Most folks in the world would call them dry holes, but we've learned to be very conservative of water use, but you can see that the amount of heat in that quantity of water would never warm a house.

The next phase for me is to put in one 300' loop of a field of loops I hope to install, hook it up to the 1 ton heat pump, monitor soil temperatures near the pipe and water temperatures entering and leaving the heat pump and try to get a fix on how many ground loops will be required. I think I'll be able to base predictions on data I collect from a straightforward but simple installation. Meanwhile, I'll keep reading the Forum. Many thanks for your comments, mm

AC_Hacker · 03-31-13, 02:11 AM

Quote:

Originally Posted by michael

...I continue to struggle with knowing how to size the heat pump...

OK, there was another poster who felt that sizing information was critically missing from the Manifesto. I was kind of hoping that he would jump in and share his knowledge, but no love...

* * *

Your house will lose heat. Your task will be to provide heat at the same rate at which heat is being lost, thus maintaining a comfortable temperature inside.

Going deeper, your house will inevitably lose heat to the great heat sink in the sky. The rate of heat loss will be dependent on the difference between the inside temperature and the outside temperature (AKA: 'Delta-T'). This Delta-T will be working through the materials your house is built of, and the resistance these materials have to heat flow. The various materials and their different heat flows can be a pretty complicated situation. There are various way to know what the heat loss will be, one way is to actually measure the amount of heat that is required to maintain comfort under actual conditions. I have done this here at my house. On a very cold winter day, I used only electric resistance heaters, with Kill-a-Watt meters attached to each heater, and logged the results. This has provided me with my heat loss 'Gold Standard', and I use this to measure the effectiveness of various Heat Load Calculation programs. I feel that this method is the most reliable because I was able to actually measure the heat loss in an actual situation. The calculation programs are all pretty good.

But let's just say that your known heat load on a cold winter night was 18,000 BTU per hour.

To keep things simple, you would select a compressor capable of producing 18,000 BTU/hr. Since 1-Ton of HVAC capacity is 12,000BTU/hr, 18,000 BTU would be 1.5 Tons. That is what capacity you'd look for in a compressor. You would also need to make a decision as to what refrigerant you want to use, as compressors are built to work best for a particular refrigerant. Let's just say you selected R22 as you refrigerant.

Your compressor will need some kind of metering device, either a cap tube or a TXV. There are tables that can be used to guide you along the way to select the cap tube or tubes you would need, for the refrigerant of your choice, like R22. Cap tube selection can be complex, but once correctly sized, they work pretty well. The reason they proliferate in commercial units is that they are very cheap to manufacture.

If you wanted to use a TXV, it would be pretty straight forward, just select the size you want, and the application for which it would be intended, heat pump in this case, and finally the refrigerant, R22 in our example.

Then you need to choose HXs. I will assume that the HXs will be used for water-refrigerant. You'll need to choose your HXs, one for evaporation, one for condensing. HXs are rated for the BTU/hr or Tons of refrigeration. Be aware that some HXs are advertised for their capacity in a water-water application, and that may not come very close to their performance in Refrigerant-water. Look for charts or computer programs that will guide you on this.

This is an over-simplified procedure, but it can get you started. There are many fine points that will lead to better performance. Learn all you can from everyone you can.

Quote:

Originally Posted by michael

...and how to design and size the source pipe array, but every day I read folk's posts brings me closer to a solution.

You will probably find, as I did, that building the heat pump is really the easiest and least expensive part of the whole project.

Soil conditions vary widely from on area to another. I can't overstate the importance of seeking local expertise on this part of the project.

Also, as I have said previously in the Manifesto, IGSHPA has the deepest lore on the art and craft of GSHP. They have excellent manuals HERE. You would be giving yourself a very generous present if you purchased this book from them.

NOTE: I have absolutely no connection to this organization, but I do recognize excellent information when I see it.

...to be continued,

-AC

jeff5may · 03-31-13, 08:31 AM

Michael,
While viewing your attic pics, I couldn't help but notice something. You have a big ridge vent fan. To achieve your water heating goal, you could place your hx assembly at the intake of the ridge vent. When temps get high enough, you could rig a small circulator pump to activate in tandem with the ridge vent, harvesting the hot attic air and depositing it into the battery of your choice. The attic would vent as originally designed, and the setup would be cheap and reliable.

03-30-13, 01:44 AM	#1452
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	I've begun collecting data from my little E-Tech 1-ton water-to-water heat pump (originally mentioned in another thread; photo below as a reminder). The source water comes into the device at 57 degrees and exits at about 48. I can increase the difference by throttling down the water flow somewhat, but it requires no less than 2 gpm, and that's about where it stands with a difference of 10 degrees. The heated water comes out about ten degrees hotter than when it enters the heat exchanger, and if I reduce that flow, I can get a 15 degree difference, but that's it. Clearly this heat pump cannot be connected directly to a radiant floor but will require a sizable buffer tank first to allow it to get the water temperature high enough to warm a floor, and second, to build up a cushion of stored heat for periods of high demand. I'm beginning to grasp how important it is to size a heat pump carefully to the size and heat rentention rate of a particular house. This particular heat pump was built to be a water heater either with an indirectly fired water tank or with an electric or gas tank that had been converted, and it would still be a good candidate for that. A little studying has convinced me that heating DHW, at least for my family, is the absolute least of our heating worries, and pales by comparison to heating the house. Because we are in a controlled water district even though we have our own well, we monitor and report our water use every month. We use an average of 60 gallons of water per day for all domestic use, i.e. drinking, cooking, washing, bathing, etc. Of that 60 gallons, only a portion is heated, and I would estimate that at 20 gallons a day. That would consume about 1/10 gallon of diesel in our water heater with an annual cost of less than $150. I'd be happy to save some of that $, but it's clear to me that going to extreme measures to reduce DHW heating cost is putting effort in the wrong place. Got to get house heat, which is more than ten times the cost of DHW, under control, and that's why I'm chasing after the idea of a GSHP. Attached Thumbnails

03-30-13, 05:15 AM	#1453
cbearden Helper EcoRenovator Join Date: Aug 2011 Location: AR Posts: 39 Thanks: 11 Thanked 4 Times in 2 Posts	AC, Michael, I noticed in his pic that the copper water exchanger in the back looks like the water wouldn't have enough length to exchange more heat to gain more efficiency out of the water heating that Michael is speaking of. Would a heat exchanger similar to what you've used be more efficient for what he's doing? Attached Thumbnails

03-30-13, 03:38 PM	#1454
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	Thank you all once again for this long, rich thread; it has become my main inspiration for continuing to work on heat pump system design. I continue to struggle with knowing how to size the heat pump and how to design and size the source pipe array, but every day I read folk's posts brings me closer to a solution. In addition to the heat pump system per se, I'm working on a heat sequestration idea which I suspect is not novel, but holds some promise for my situation. Our house has a large attic that collects a great deal of heat on even overcast days. I propose to collect that heat and store it in the same ground field that the heat pump will use for its source. I've conducted some crude experiments, illustrated below in photographs, and I can obtain more than half the heat I need for our house from the attic space, but the difficulty has always been that, in general, we don't need the heat during the day when it's available. One 80 or 120 gallon tank of hot water can be collected pretty quickly, but it won't be nearly enough to keep the house warm through the evening and night. In another post I have referenced collecting data on soil temperature and heat movement in soil. I have discovered that heat moves quite slowly through the soil. I could circulate 60 to 110 degree water from the attic to the soil in the location of the source pipes, and heat absorbed by the soil from the source piping won't dissipate far from the pipe in the few hours until it is needed in the evening when the attic circulation system would shut down and heat pump system would start up. In this manner I could recharge the soil heat bank any time the temperature in our attic rose to above 55 degrees The photos below show two attempts to salvage heat from the attic, and they proved equally effective. I circulated water during warm periods and collected the heat in a 55 gallon drum in order to measure potential BTU/h gain from the attic, and I felt the results were heartening enough to merit development. System one utilizes slinky type coils held off the roof sheathing enough so that re-roofing wouldn’t endanger the coils. The coils were connected in series and covered with reflective mylar backed by 1” styrofoam. There is lots of space for such heat exchangers, but I installed only four panels for the experiment. System two utilizes a fan coil and crude duct work that draws air from the attic peak and blows the cooled air down toward the floor of the attic. One small fan coil collected as much heat in a given time period as did the four coils of polybutylene, and it seems a much simpler solution. It also has the advantage of avoiding trapping heat next to the roof sheathing. As long as the attic air temp remains above the soil temp near the source pips, heat can be sequestered in the soil until needed. It seems to be the case that nearly all the heat near the surface of the earth, say within the first few hundred feet, comes from solar radiation, and only a small amount comes from geothermal heat migrating to the surface. By sequestering heat from my attic in the ground, I’d only be boosting the normal activity of the sun and providing easy access for removal via the heat pump. Attached Thumbnails

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

03-30-13, 04:00 PM	#1455
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	I would pump the water down to a 120gal hot water tank (or as big as you can get) and then pump that water to the HP at night through a 3 way valve to limit the water temp from going higher than say....60F. That roof could be a big solar collector if you want it to be. The other benefit is that the ground will have more time to regenerate naturally. I am not a big fan of underground storage unless it is designed right. (look up Okatokes, Alberta solar geo system). When the tank comes down in temp to the ground temp, switch over with a diverting valve. Some people have tried to do single home systems dumping the heat directly into the ground near the piping but other then a good heat dump, it wasn't overly effective. Dumping the heat into the liquid was more so.

03-31-13, 12:33 AM	#1458
michael Michael Join Date: Feb 2013 Location: mendocino, california Posts: 67 Thanks: 7 Thanked 2 Times in 2 Posts	Hello AC, You won't be getting into any fist fight with me! I couldn't agree more, if for no other reason than that the designers of the heat pump had the balance you speak of in mind when they sized the heat exchanger and the circulating pump. And I think we're in agreement on the second comment as well. When I wrote "cushion of stored heat...demand," I pictured higher demand causing a kind of rapid cycling of the heat pump that would be smoothed out if it could operate on a larger mass of water. I'm using the "pump and dump" concept here while I'm checking out the operation of the heat pump, but that's only because I don't have a closed source of water for heat, and I'm pumping and dumping from a 5000 gallon water storage tank, not between wells. I can't give a definitive answer to the question about local restrictions, but my gut tells me what with how touchy everyone is about water here, there'd be a lifetime of hoops to go through. Another reason it may not be a workable idea here is the sheer quantity of water required. One of our wells produces 75 gallons a day, and the other about 100 per day. Most folks in the world would call them dry holes, but we've learned to be very conservative of water use, but you can see that the amount of heat in that quantity of water would never warm a house. The next phase for me is to put in one 300' loop of a field of loops I hope to install, hook it up to the 1 ton heat pump, monitor soil temperatures near the pipe and water temperatures entering and leaving the heat pump and try to get a fix on how many ground loops will be required. I think I'll be able to base predictions on data I collect from a straightforward but simple installation. Meanwhile, I'll keep reading the Forum. Many thanks for your comments, mm

03-31-13, 08:31 AM	#1460
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Michael, While viewing your attic pics, I couldn't help but notice something. You have a big ridge vent fan. To achieve your water heating goal, you could place your hx assembly at the intake of the ridge vent. When temps get high enough, you could rig a small circulator pump to activate in tandem with the ridge vent, harvesting the hot attic air and depositing it into the battery of your choice. The attic would vent as originally designed, and the setup would be cheap and reliable.