Converting heat pump to make hot water?

Number21 · 03-27-14, 08:37 AM

Hello everyone. I have a shop for my business and we generate excess heat in a proprietary process. For this we need to install about 2-3 tons of air conditioning. I would like to make hot water with this waste heat so that I can use it for heating in other parts of the building.

This will all be kind of experimental and I don't want to spend a ton of money. I notice on craigslist I can find a smaller household type heat pump for $500 or less.

Can I simply braze on a flat plate heat exchanger in place of the condenser coil and make hot water? How warm of water can I make while still efficiently providing A/C? Somewhere around 120F?

stevehull · 03-27-14, 08:50 AM

It would be helpful to know if the generated heat is in the form of hot air (which I suspect). Realize that water has a heat capacity density 1,000 times that of air. In other words, you can put a LOT of heat into water without increasing the water temperature very much.

The key is to capture the heat . . .

Can you provide a few details so that we could understand this? For example, can the heat generating machine be put in a specific room? That would allow a heat pump to work just in that area.

If the heat is too diffuse, and hard to capture, you can always blow it away literally with air. A large efficient fan can bring in outside air to cool off the area.

The key is to homebrew this as buying a commercial product would be FAR to expensive for you to justify a purchase.

A few more details will help - and welcome to the group!

Steve

NiHaoMike · 03-27-14, 08:52 AM

Your best bet is to add a desuperheater coil.

AC_Hacker · 03-27-14, 10:45 AM

Quote:

Originally Posted by Number21

...Can I simply braze on a flat plate heat exchanger in place of the condenser coil and make hot water? How warm of water can I make while still efficiently providing A/C? Somewhere around 120F?

Number21,

I think you have the right idea.

Forget about a desuperheater coil, that will be going in the wrong direction.

Since it takes 2 or 3 Tons of air conditioning to extract the heat, you need 2 or 3, 1-Ton air conditioners (or 2ea 1.5 Ton) to do the job. And yes, brazing flat plate HXs in as condensers, and circulating water to an area where you need heat is a great idea.

And yes, you should be able to make water as warm as 120 degrees F.

Although this may not be a trivial project, I highly encourage you to do this.

By the way, if your business is in or near PDX, I could come by and take a look... You can contact me via email HERE.

There might even be some remarkably easier solutions!

Best,

-AC_Hacker

Number21 · 03-27-14, 07:48 PM

Yes, the heat is in the form of hot air, coming from a 1000sq ft closed room. Basically my cooling needs are very similar to a small house on a hot day. I need to keep the air inside about 75-80 degrees and I calculate roughly 30,000 BTU of heat output.

Quote:

Originally Posted by AC_Hacker

Since it takes 2 or 3 Tons of air conditioning to extract the heat, you need 2 or 3, 1-Ton air conditioners (or 2ea 1.5 Ton) to do the job.

Why is that? I thought I wanted one single 3 ton heat pump? My heat load will be pretty constant, so I don't ever really need to lower the output.

I'm starting to think I might just buy a new heat pump. I can't post a link because I don't have enough posts on this forum yet but I found a 3 ton Goodman R-410A system with a coil for $1100. That seems really cheap.

Quote:

Originally Posted by AC_Hacker

By the way, if your business is in or near PDX, I could come by and take a look... You can contact me via email

Thanks for the offer! We'll see how far I get, I've wanted to experiment with a system like this for quite a while, not really sure why. LOL

Is it difficult for a DIYer to install and charge a heat pump? I've got the plumbing and electrical part covered but I've never tried to charge an A/C system before...

AC_Hacker · 03-27-14, 08:18 PM

Quote:

Originally Posted by Number21

...Is it difficult for a DIYer to install and charge a heat pump? I've got the plumbing and electrical part covered but I've never tried to charge an A/C system before...

It's all here on the forum.

Just use the search engine, it will take you to all the info you need.

Sounds like you don't need any hand-holding, right?

-AC

Number21 · 03-27-14, 08:39 PM

Would it be possible to install valves on the heat pump to allow me to choose whether I want it to be air cooled or water cooled? In the summer I won't need the heat so I will need to vent it outside. Would be nice to just use the heat pump as normal instead of using a radiator to cool the water in the summer.

jeff5may · 03-27-14, 07:46 PM

I understand the whole "proprietary process" thing with businesses. I literally shred 100+ pages of "proprietary" blueprints a week, after my whole team has had our ways with them. If anyone decided to take any home, no one would notice, kind of like scrap metal slugs. It's not the "cash cow" I find useless, just the notion that a cow is a secret weapon to make money. Like the "secret sauce" at fast food joints: you can buy it by the gallon at Sam's Club...but only if you know what IT is. Just buy the ingredients at different stores so you don't end up in fast food court.

Meanwhile, the key is to capture THE HEAT...

Is it solid, liquid or gaseous heat?

What temperature and volume values are we dealing with?

If it is high volume, low grade heat, a heat pump will do well.

If it is low volume, high grade heat, an alternate transport method may be more efficient.

NiHaoMike · 03-27-14, 09:31 PM

You can use a small evaporative cooling tower (possible to DIY out of an evaporative cooler and some copper tubing) and turn it into a hybrid. It would actually be more efficient than a regular air cooled condenser.

jeff5may · 03-28-14, 03:52 AM

Some hot deals from random places in oregon:

2004 4 ton used performance heat pump

Air Conditioner

**WATER HEATER HEAT PUMP(NEW IN BOX)**

Heat Pump

free standing air conditioner

Your area seems to be a virtual zombieland of HVACR units in limbo. AC has had random orphans just show up at his doorstep. There seems to be an eternal supply. Even if you live in the country, I'm certain you can find a unit to do surgery on for under $50 per ton of refrigeration. Maybe 100 per ton less than 2 yrs old. Look and you will find.

03-27-14, 08:37 AM	#1
Number21 Lurking Renovator Join Date: Mar 2014 Location: Oregon Posts: 13 Thanks: 0 Thanked 0 Times in 0 Posts	Converting heat pump to make hot water? Hello everyone. I have a shop for my business and we generate excess heat in a proprietary process. For this we need to install about 2-3 tons of air conditioning. I would like to make hot water with this waste heat so that I can use it for heating in other parts of the building. This will all be kind of experimental and I don't want to spend a ton of money. I notice on craigslist I can find a smaller household type heat pump for $500 or less. Can I simply braze on a flat plate heat exchanger in place of the condenser coil and make hot water? How warm of water can I make while still efficiently providing A/C? Somewhere around 120F?

03-27-14, 08:50 AM	#2
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	It would be helpful to know if the generated heat is in the form of hot air (which I suspect). Realize that water has a heat capacity density 1,000 times that of air. In other words, you can put a LOT of heat into water without increasing the water temperature very much. The key is to capture the heat . . . Can you provide a few details so that we could understand this? For example, can the heat generating machine be put in a specific room? That would allow a heat pump to work just in that area. If the heat is too diffuse, and hard to capture, you can always blow it away literally with air. A large efficient fan can bring in outside air to cool off the area. The key is to homebrew this as buying a commercial product would be FAR to expensive for you to justify a purchase. A few more details will help - and welcome to the group! Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

03-27-14, 08:52 AM	#3
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	Your best bet is to add a desuperheater coil. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

03-27-14, 09:31 PM	#9
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	You can use a small evaporative cooling tower (possible to DIY out of an evaporative cooler and some copper tubing) and turn it into a hybrid. It would actually be more efficient than a regular air cooled condenser. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

03-28-14, 03:52 AM	#10
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Some hot deals from random places in oregon: 2004 4 ton used performance heat pump Air Conditioner WATER HEATER HEAT PUMP(NEW IN BOX) Heat Pump free standing air conditioner Your area seems to be a virtual zombieland of HVACR units in limbo. AC has had random orphans just show up at his doorstep. There seems to be an eternal supply. Even if you live in the country, I'm certain you can find a unit to do surgery on for under $50 per ton of refrigeration. Maybe 100 per ton less than 2 yrs old. Look and you will find. Last edited by jeff5may; 03-28-14 at 03:59 AM..

03-27-14, 08:39 PM	#7
Number21 Lurking Renovator Join Date: Mar 2014 Location: Oregon Posts: 13 Thanks: 0 Thanked 0 Times in 0 Posts	Would it be possible to install valves on the heat pump to allow me to choose whether I want it to be air cooled or water cooled? In the summer I won't need the heat so I will need to vent it outside. Would be nice to just use the heat pump as normal instead of using a radiator to cool the water in the summer.

03-27-14, 07:46 PM	#8
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	I understand the whole "proprietary process" thing with businesses. I literally shred 100+ pages of "proprietary" blueprints a week, after my whole team has had our ways with them. If anyone decided to take any home, no one would notice, kind of like scrap metal slugs. It's not the "cash cow" I find useless, just the notion that a cow is a secret weapon to make money. Like the "secret sauce" at fast food joints: you can buy it by the gallon at Sam's Club...but only if you know what IT is. Just buy the ingredients at different stores so you don't end up in fast food court. Meanwhile, the key is to capture THE HEAT... Is it solid, liquid or gaseous heat? What temperature and volume values are we dealing with? If it is high volume, low grade heat, a heat pump will do well. If it is low volume, high grade heat, an alternate transport method may be more efficient.