The Homemade Heat Pump Manifesto

[Marc_NL]

Hi all, Marc here from the Netherlands.

I found this forum and thread while searching for a way to convert a airconditioning unit / ASHP to ground sourced. The vast number of pages here kept me busy for a while but now is the time to start sharing.

First of is the reason for wanting to do a conversion. Overhere there are quite a few GSHP manufacturers available and they all have one thing in common: being very expensive. The reason for this seems to be the low volume and the niche market in which they operate. Building a low-energy or passive house is quite expensive so people willing to invest in this are probably also willing the cough up some extra cash for the heatpump. I, however, do not see a good reason for these units being at least triple the price of a comparable ASHP. Also, the modern ones (inverter drive) are even more expensive. Two options then remain, getting a cheap unit from China which will probably work just as well or converting a unit to ground source operation.

We are preparing a new build to passive house standard. This makes sure we should be able to use a relatively low power heat pump. The source will be either a number of shallow (some 30' to 40') vertical holes or just a horizontal heat exchanger at some 5' to 7'. This I can do myself and save quite a bit there already.

As plans progress I will work out the heat load we will be seeing. For now according to passive house standard (max 15W/m2) we get a max heat load of 3kW. On top of this we will need a bit of heat for the garage (not as well insulated, but also not requiring 68F) and the DHW. In general for passive houses the rule seems to be that we'll need about half of the annual heating energy for DHW and the other half for house heating.

The heat will be delivered with underfloor heating, either in a separate cement layer or as part of the construction (active concrete). Therefore quick temperature changes might need to be covered through heating of ventilation air to the open kitchen / living room area.

The whole reasoning for wanting a heat-pump is to make sure we do not need to be connected to the natural gas distribution for which we'd have to pay a fee to connect and then a monthly fee as well as the actual use of gas. However in this country the electricity is made extra expensive, currently at some E 0.23/kWh. Natural gas comes in at around E 0.60/m3. With 1 m3 of natural gas giving about 10 kWh, we need at least a COP of 4 for this to make sense from a budget standpoint. With the setup described above this should be achievable for the heating, but not for DHW. Not sure what to do there yet, maybe a small heatpump in cascade with the main one for hot water? Or just use solar hot water during a large time of the year and take the low COP for granted in winter?

I'll be looking for a modern inverter driven unit to convert. Most of them run R410A, some run R407C. From my quick investigations on this R410A seems to run higher pressures, so I could better look for a R407C unit. Or do you guys think that running lower pressure is not detrimental to the compressor efficiency? I plan to run R290 in the new unit. With R407C closer to R22, it seems to make sense, no?

I'm aware of the arguments against R290 from a flammability standpoint, however I can't be bothered. Almost every house here is connected to the natural gas distribution for both heating and cooking. Some explosions happen every year, but the majority of them is during ground work (hitting the gas pipe during excavation) or deliberate (suicide). Also we run a good number of cars on LPG (liquified propane) and LNG (liquified natural gas) without incidents. If we are not worrying about this, why would I need to worry about R290 in a closed circuit? The technical room will be well ventilated though.

Any input on the R410A vs R407C matter? Or on increasing COP for DHW?

Thanks!

[Daox]

Welcome to the site Marc. You've certainly come to the right place.

[AC_Hacker]

Originally Posted by Marc_NL

Hi all, Marc here from the Netherlands.

Hello Marc! Glad you are part of our conversation.

Your plans all sound perfectly reasonable to me. If you are planning a house that approaches Passive House standards, you are working in exactly the right direction. Supplementing Passive House design with its high COP and using modest GSHP as supplementary heat is a very intelligent way to go.

Originally Posted by Marc_NL

The vast number of pages here kept me busy for a while but now is the time to start sharing.

Sorry about the large number of pages, but there is much to know.

Originally Posted by Marc_NL

First of is the reason for wanting to do a conversion...

Your reasoning about energy costs is also applicable here in the US also, but your costs are even higher, so the reasons for you to proceed in your direction are even more compelling.

Originally Posted by Marc_NL

We are preparing a new build to passive house standard. This makes sure we should be able to use a relatively low power heat pump. The source will be either a number of shallow (some 30' to 40') vertical holes or just a horizontal heat exchanger at some 5' to 7'. This I can do myself and save quite a bit there already.

It is just great that you want to undertake this. There is a book, CLGS Installation Guide (#21020), that has a huge amount of information, gathered over many years. It's cost is such a small fraction of the money you will invest in your home, I strongly recommend it to you.

The various conditions of the soil in your location will have a major impact on which technique you choose. I happen to live in an area that is built upon the deposits of glacial debris of ancient ice ages, and this has made drilling very difficult, and trenching is most often a much better alternative. On the other hand, we have people who are from the state of Mississippi, who have the good fortune of having an easily-drilled clay & sand soil structure. This depends on your area and you will need to seek out local knowledge.

Originally Posted by Marc_NL

As plans progress I will work out the heat load we will be seeing. For now according to passive house standard (max 15W/m2) we get a max heat load of 3kW. On top of this we will need a bit of heat for the garage (not as well insulated, but also not requiring 68F) and the DHW. In general for passive houses the rule seems to be that we'll need about half of the annual heating energy for DHW and the other half for house heating.

I am very glad that you are aware of the fundamental aspect of heat load. Too many people plunge into an endeavor like yours without this extremely important consideration. To not be aware of your heat load is like shooting an arrow, hoping to hit the target, without knowing where the target is! I think you are on the right path.

Originally Posted by Marc_NL

The heat will be delivered with underfloor heating, either in a separate cement layer or as part of the construction (active concrete). Therefore quick temperature changes might need to be covered through heating of ventilation air to the open kitchen / living room area.

Daily Heating Degrees, Zwolle, Neatherlands

This topic is very interesting to me, and my thinking about this has gone through several revisions since I started the 'Manifesto' thread.

Essentially, if you live in a climate where the winters go cold and stay cold, with only minor deviation, then high-mass heating makes excellent sense. However, if the heating-season temperatures fluctuate greatly, you will prefer your heat to come from low mass heating, which is able to change rapidly to accommodate ambient conditions.

You didn't mention where in NL you live, but I looked up the heating degree days in Zwolle, Neatherlands, as recorded at the Groningen Airport Eelde, NL (6.58E,53.12N). I looked at daily Heating Degree Days over the last year, and above you can see on the graph, that the winter temperature swings are significant. If you weather is not like Zwolle, you can find out for you exact location.

But the graph does suggest to me that you may want to keep temperature fluctuations in mind as you proceed.

There is another aspect to this... If your house is extremely well insulated, it will not be as severely affected by short-duration ambient changes. This can influence your approach.

If you are designing your house yourself, the Passive House Planning Package (PHPP) should have a data base which contains historical data from your own area, which should help your decisions. You should definitely seek this tool out.

Originally Posted by Marc_NL

The whole reasoning for wanting a heat-pump is to make sure we do not need to be connected to the natural gas distribution for which we'd have to pay a fee to connect and then a monthly fee as well as the actual use of gas. However in this country the electricity is made extra expensive, currently at some E 0.23/kWh. Natural gas comes in at around E 0.60/m3. With 1 m3 of natural gas giving about 10 kWh, we need at least a COP of 4 for this to make sense from a budget standpoint.

COP 4 is not so easy to achieve.

Originally Posted by Marc_NL

With the setup described above this should be achievable for the heating, but not for DHW. Not sure what to do there yet, maybe a small heatpump in cascade with the main one for hot water? Or just use solar hot water during a large time of the year and take the low COP for granted in winter?

Right now, there is a very interesting project going on by a fellow EcoRenovator who lives in Mississippi. He is building a very small 'direct expansion' GSHP water heater for domestic use (DWH). His project is attracting great interest by my fellow DIY friends who really inderstand the potential in what is being developed. You should look at this project.

Originally Posted by Marc_NL

I'll be looking for a modern inverter driven unit to convert. Most of them run R410A, some run R407C. From my quick investigations on this R410A seems to run higher pressures, so I could better look for a R407C unit. Or do you guys think that running lower pressure is not detrimental to the compressor efficiency? I plan to run R290 in the new unit. With R407C closer to R22, it seems to make sense, no?

In my opinion, all of yor thinking here is good. However, the inverter heat pumps are much more complex than the simpler, non-inverter types. We have had several people tackle the complexity of an inverter conversion, and to date there have been no reports of a successful conversion. If you are an engineer with the proper equipment and experience to analyze the logic of the signals that issue from an inverter heat pump, you stand a chance of success. I think I speak for every serious heat pump hacker here, "We all would be enormously grateful to anyone who could 'crack the code' of these wonderful machines."

Originally Posted by Marc_NL

Any input on the R410A vs R407C matter?

If you're going with R290, R410a machines are not the best match.

Best of luck in your project. Keep us informed as you proceed, and remember to take lots of photos. And don't forget, sharing your mistakes can be every bit as important as sharing your successes.

-AC_Hacker

[NiHaoMike]

Looking the other way, maybe you could consider a CHP setup and going off grid? That might make sense if there's a significant service charge for electricity.

[Marc_NL]

Thanks for the welcoming and the positive and constructive feedback guys, well appreciated.

Originally Posted by AC_Hacker

The various conditions of the soil in your location will have a major impact on which technique you choose.

One of the first things on the agenda for the house build is a soil survey. This needs to be done to provide information to the construction engineer about the ground build-up and the load it can carry. I'm not too sure how deep they will go, but expect at least some 20m. This will give a first indication of soil conditions for the heat exchanger as well.

Originally Posted by AC_Hacker

There is another aspect to this... If your house is extremely well insulated, it will not be as severely affected by short-duration ambient changes. This can influence your approach.

If you are designing your house yourself, the Passive House Planning Package (PHPP) should have a data base which contains historical data from your own area, which should help your decisions. You should definitely seek this tool out.

Up till now I have used the PHVP tool, which is a skinned down version of the PHPP. We'll need to see whether the architect or myself will do the PHPP. It is a great tool as it gives the heat loss and the heat gain separately. From what I can see now the variation in outside temperature has less of an effect as the heat gain (passive solar gain). As you've also mentioned in this thread floor heating is particularly effective because of the large area involved. This means that a relatively low temperature is needed (a few degrees above required indoor temperature). One of the biggest benefits I see here is that as soon as the indoor temperature rises a few degrees (due to solar gain) the floor (and ceiling) stops giving heat and starts absorbing it. I'll need to work on it some more, but this feeling seems to be backed up by comments from people with houses using active concrete (very few actually in use though).

Originally Posted by AC_Hacker

If you are an engineer with the proper equipment and experience to analyze the logic of the signals that issue from an inverter heat pump, you stand a chance of success.

I'm not too sure what has been done in this field already so I might just be overly optimistic about this. My idea for the moment is that these units must come with temperature and pressure sensors for the controls to work well. Therefore they should already be able to give the right information to any other control signal which would need to be build (I can't imagine the original controls would work well if half the parts are cut off etc). I'm an electronics engineer and feel comfortable enough to make the hardware and write a little program to run it. However I would surely need support on coming up with a good control strategy / algorithm.

Originally Posted by NiHaoMike

Looking the other way, maybe you could consider a CHP setup and going off grid? That might make sense if there's a significant service charge for electricity.

Thanks, I did consider it sometime ago, getting an aircraft APU or ground unit and make it supply my house. However we are required to be connected to the grid overhere, so I'll have to pay for this anyway. Also when using PV panels the grid is an excellent buffer. For CHP I would need my own batteries or some form of storage.

So practically running no gas but electricity only seems the best way forward.

[AC_Hacker]

Originally Posted by Marc_NL

I'm not too sure what has been done in this field already so I might just be overly optimistic about this. My idea for the moment is that these units must come with temperature and pressure sensors for the controls to work well. Therefore they should already be able to give the right information to any other control signal which would need to be build (I can't imagine the original controls would work well if half the parts are cut off etc). I'm an electronics engineer and feel comfortable enough to make the hardware and write a little program to run it. However I would surely need support on coming up with a good control strategy / algorithm.

Marc_NL,

I certainly don't want to discourage you from hacking an inverter mini-split, it would be a great thing for all of us if someone has success.

However, you do have a very large project ahead of you, and in my opinion, you will want to choose your battles wisely.

An older tech single speed unit has respectable efficiency, and is fairly easy to hack. The remaining structures that connect it to your house can be re-used, should you "crack the code" on an inverter tech unit later.

But I just did a search over EcoRenovator, and I came up with two links that apply to hacking an inverter technology (variable frequency) compressor.

The first link is to a thread started by Acuario, who apparently is an electronics applications designer. Acuario's thread is very informative and it has a fairly good in-depth info on how the two parts of the mini-split communicate.

To my knowledge, Acuario was not completely successful with the inverter tech approach, although he has enjoyed multiple successes with single speed units.

http://ecorenovator.org/forum/geothe...r-machine.html

The second link was started by randen, not a circuit designer, but definitely a very capable DIY guy. He is a tool designer and tool maker, with extensive machine experience. His approach was to bypass the 'black box' inverter tech thing. Instead, he used available "off the shelf" variable speed components:

• Three Phase Compressor
• Variable Frequency Drive

Randen's unit is working, and it is working very well.

http://ecorenovator.org/forum/geothe...shp-build.html

If you don't find what you're looking for in their threads, you can contact them through EcoRenovator Private Message. They are both very good people to know.

Best,

-AC

[randen]

Marc_NL

I like where your going with this. A clean slate, building a passive house and utilizing GSHP for your heating. Contemplating off grid capabilities. I'm almost certain at this point with our current technologies and economies of scale it will make financial sense.

1/ building a passive house using a minimum of heat energy to remain comfortable HUGE!. Building materials of high quality are available and at a reasonable cost.

It was a common topic here in Canada Ontario when I was building 20 yrs ago "Over insulating and premium triple glazed windows for your new home and with energy prices what they where, you would never see a return on your investment????" Well that theory didn't work!! Now with the energy costs plus the service costs and any thing else they can bill you for, People only wish they could cut the cord.

2/ DIY a heat pump. Yes it is very do-able. But a huge amount of work. Ask me how I know. That's why the costs to purchase one may seem a little much. As for building a electronic control for your DIY machine. I think I my humble opinion is entirely Un-warranted. They are so efficient anyway. (there's such a thing as over controlling and or over-complicating). Even the Variable frequency Drive maybe a little over-kill for a smaller unit.

3/ Combination of heated floors and Heat-Pump STELLAR!! I would suggest to install in the floor dedicated loops (plastic tubing in-expensive--Heat exchangers not so) A loop for your heat pump and one for your solar hot water.
Controlling different zones in the floor Not Required again over-controlled and added costs for valving etc.

4/Passive house, Zero Energy, Off Grid, Solar Powered TOTALLY Possible. And at this point of time I believe financially realistic. --Heat pump or solar hot water operating during the sun lighted hours--warming a concrete floor (heat battery) Keeping you warm though the night in a home that can retain that heat. Yes very possible. Solar voltaic panels and inverters-reasonably priced. Lithium storage batteries commercially available. LED lighting. energy efficient appliances yes.

Nice project!!

Randen

[AC_Hacker]

I thought it might be interesting to look at the degree day graphs (daily) for London, Ontario (very near randen) and Zwolle, Neatherlands (possibly near Marc_NL):

Heating Degree Days (daily) for Zwolle, Neatherlands




Heating Degree Days (daily) for London, Ontario

The things that jump out at me are the differences in the "depth" of winter. In other words, the amount of heating that would be required in each location. The other thing I see is the amount of variation in heating requirement for each location.

[* EDIT: I also added the HDD chart for Portland, Oregon. *]

Heating Degree Days (daily) for Portland, Oregon

Best,

-AC

[Marc_NL]

Originally Posted by AC_Hacker

However, you do have a very large project ahead of you, and in my opinion, you will want to choose your battles wisely.

Ok, thanks, agreed. My direction of thought wasn't to use the existing controls and try to communicate with them. I'd leave the system to actually be quite simple, only differing parts from fixed speed would be the inverter to drive the compressor and the electronic expansion valve. The latter could be omitted at first and just using a thermal one would be the alternative. The positive thing on sourcing a inverter unit would be that it'll have a load of parts which can be used directly for monitoring and later on for control if needed, wanted etc.

For parts and tools I'm following two online auction sites (mostly liquidation sales). Currently there are a bunch of Danfoss GSHPs for sale, ending June 9th. This is very rare and I hope the interest is low (there are 3 5.7kW units available which would only be suitable for passive houses and the like). So if I come across a good deal on something like this, I will take it. Very much in line with the 'choose your battles wisely' philosophy ;-). There are many battles in the overall project.

Originally Posted by randen

1/ building a passive house using a minimum of heat energy to remain comfortable HUGE!. Building materials of high quality are available and at a reasonable cost.

Yes, passive house standard is the way forward. Energy not being needed keeps cost down regardless of what the government or energy companies do. However, passive house building is still an oddity here. We have a very traditional build industry and the only changes it seems to make are for satisfying the regulations, not the customers. This makes such an endeavour difficult.

Originally Posted by randen

2/ DIY a heat pump. Yes it is very do-able. But a huge amount of work. Ask me how I know. That's why the costs to purchase one may seem a little much. As for building a electronic control for your DIY machine. I think I my humble opinion is entirely Un-warranted. They are so efficient anyway. (there's such a thing as over controlling and or over-complicating). Even the Variable frequency Drive maybe a little over-kill for a smaller unit.

Thanks. I've been reading your thread on the 5 ton VFD unit, great work there! I agree on this comment as well as the one made by AC_Hacker. Just a variable speed on the compressor (and later on the pumps as well) could be the right direction, first starting with fixed speed. As to the amount of work, please note that I have my eyes open for good deals on commercial units, however, they are rare.

Originally Posted by randen

3/ Combination of heated floors and Heat-Pump STELLAR!! I would suggest to install in the floor dedicated loops (plastic tubing in-expensive--Heat exchangers not so) A loop for your heat pump and one for your solar hot water.
Controlling different zones in the floor Not Required again over-controlled and added costs for valving etc.

I'll have to continue the PHVP work but I think solar heating of the floor is of limited use, the power entering through the glazing could well be close to what would be needed during most of the year. For hot water the situation is different ofcourse. Indeed we won't control different zones, the house will naturally reach a near constant temperature. The situation of the rooms is such that the warmer ones (kitchen / living) are located south to benefit from solar heat. The cooler ones are up north. Also those thermal wax valves do consume considerable power.

We don't see off-grid as realistic yet. The grid is actually a cheaper battery than one we could buy. It could change over the years however. PV will surely by part of the house as well, trying to reduce nett electricity use to zero.

I still have some work ahead on the heat recovery ventilation as well. The idea is to run brine through a water to air heat exchanger for air entering the house. This should prevent the heat recovery system from freezing during the cold winter days. For extra (quick) heating to take care of sudden thermal changes it would be good to have such a heat exchanger after the heat recovery unit and power it with the output of the GSHP. In summer this one could aid in passive cooling.

Here again the trick would be not to make things overly complicated. Also extra heat exchangers give extra resistance and thus need more power from the fans. I'll have to find the right compromise.

As you guys know an eco friendly house is a system, it'll work as well at the weakest part.

Zwolle is close enough to be relevant. It seems to correspond quite well with Portland. London is a bit chillier for sure. However, we have had two very warm / mild winters.

Cheers,

[AC_Hacker]

Originally Posted by Marc_NL

...Also those thermal wax valves do consume considerable power...

I'm not sure that I know what a 'thermal wax valve' is? I know that there are temperature-control valves that control bath and shower water temperature, that use paraffin's high thermal expansion rate as a regulatory mechanism, but they use no external power. Sounds like you are talking about something different.

Originally Posted by Marc_NL

...I still have some work ahead on the heat recovery ventilation as well. The idea is to run brine through a water to air heat exchanger for air entering the house.

I don't think that brine is being used much in North America. I'd like to know more about your interest in it, and what its advantages are.

Originally Posted by Marc_NL

This should prevent the heat recovery system from freezing during the cold winter days. For extra (quick) heating to take care of sudden thermal changes it would be good to have such a heat exchanger after the heat recovery unit and power it with the output of the GSHP. In summer this one could aid in passive cooling.

This sounds like a wonderful idea. There is a house here in my city of Portland that was very advanced for it's time, called The Rose House (full architect drawings are HERE), and it uses a very high-efficiency HRV followed by a water-to-air HX, for the very same purpose that you have in mind. Their HRV is similar to THIS_ONE. I have become friends with the owners, and they have been kind enough to let me peek into every technical aspect of their house. The house was a Zero Energy project partly funded by the state Oregon. The house has many excellent features:

• optimum orientation to the sun
• optimized roof overhang
• very intelligent architectural design
• super efficient HRV followed by water-to-air HX
• good insulation from the ground
• good insulation in the walls
• good, 2x glass windows
• windows that were each specifically designed for it's position in the house (different glass formulations & different coatings)
• Large thermal storage tank inside the conditioned envelope
• PV panels on the roof
• ASHP that took advantage of the heat from the back side of the PV panels for it's input air
• Solar water heating
• Custom designed controller to balance all of the energy resources

I went to see them a few months ago (my second visit) and I had with me all of the documentation that was available, with underlines and questions, so they realized that my interest was very serious, and they were very candid with me regarding their experience of having lived there for ten years...

First, they were utterly satisfied with the architectural aspects of the house, particularly, how the light and space were crafted to provide a home that was resonant with their lives. They repeatedly mentioned the light and space.

They were proud of the energy efficient aspects, and proudly pointed out the various parts and the role they played in the overall house.

However, toward the end of my extended visit, they became more open about their dissatisfactions. The custom controller that was designed specifically for their house, to balance all the various heat-gains and to apportion out the energy to the various heat requirements (house heat via HRV HX, radiant floor in bathroom, etc.), quickly became a total failure. It was so complex that even the firm that designed and built it were unable to make it function as it was intended. Therefore, the unusual days when it was too cold or too warm had to be dealt with by having the owner (82 years old) climb a ladder into the small attic utility room and adjust the water flow to the HRV by hand. He performed other aspects of control to the system also, but I wasn't able to witness him doing it. So, in other words, an 82 year old man is now serving the function of system balancing. His wife of 68 yrs is concerned, because her husband is the only person who understands the system.

Also, they are having trouble with the amount of heat that is being lost through the larger front windows. (3X glass would help here. I want to work with them toward a Multi Layer Insulation window shade solution). I don't think that reducing the window area is the solution, because it is the natural light that makes the house so satisfying.

Looking at the drawings for the house, I think that more attention should have been given to insulate the foundation from the ground.

I think that thicker walls would have been better.

There are many lessons to learn from all of this. Not the least of which are:

• Pay great attention to the architectural aesthetics, and how they affect the occupants.
• Design the thermal aspects of the house (especially windows), giving the "mechanicals" a smaller role.
• Pay greater attention to the foundation and floor insulation.
• If a controller is required, try to find a commodity controller, should controllers fail, or owners change.

By the way, I have been following this house with great enthusiasm, since it was built. There were many detailed pages on the Internet relating to this house, that have mostly disappeared. However, greedy EcoRenovator that I am, I have in my archives everything that was ever published about this house.

Best,

-AC