Inverter ASHP to WSHP conversion (on a boat), design&discussion
 

I will start by saying I got inspired by the home made heat pump manifesto, many thanks AC Hacker for the thread and for everyone posting very useful knowledge there. I will try to keep the information here pretty focused, the purpose of the thread is to find help/knowledge and ideas in regard to my necessary conversion.

Mission: convert a high! COP inverter driven ASHP (normal household, not marine) to a WSHP, on a boat, possibly providing water heating for showers or thermal storage too.

Why: I live on a boat, I have to heat it efficiently, I don't like open flames, noise, I don't have money for a MARINE high COP unit, I got the unit with a stupid high discount and lastly and most importantly the conversion itself needs to be done in order to remove the outside unit from my cockpit and put it in the engine compartment using water as a heat source.

Challenges: design (dimensioning HX, pumps, shower water heating circuit, electronics), sourcing parts (hard to find some parts in Europe) and manual labour (soldering).

Unit details: the heart of the unit is a DA110S1C-30FZ (R410A) compressor, it has an Electronic Expansion Valve (probably SanHua model). Unit was rated for 8000btu in heating, but on the inside and outside labels it says it goes up to 12500btu, compressor rating 160-1100w(2600-12500btuh). The COP is 5.56 in papers. The remote it came with seems pretty stupid, and the indoor unit does not have a digital display, just a bunch of leds. The unit was sold under the brand Midea, but there is absolutely no brand name anywhere on the physical unit, remote, indoor or outdoor.

The plan: swap the outdoor HX with a water to refrigerant HX, leave all (most) the electronics, sensors and controls intact. I also want to add a secondary HX for heating a water tank (but this is an optional goal=would be nice).

Immediate tasks: size the outdoor HX and source it (or the other way around), figure out the piping (adding pressure gauges&where&if), figure out the hot water tank size and location (suction vs discharge), figure out potential problems in the system. So here I would be grateful to get ideas, help dimensioning etc.

Statistics: unit pulls an average of 8kw or less/day, while heating the inside (28ft sailboat) to around 17-22 deg, outside temps around 0-8 deg Celsius. For 4 days I left the unit on 17deg, outside ran an average of 4-5 deg, pulled 22.79kw. Also, I suspect a small leak of refrigerant, not sure of it, suspicion is based on different outside unit behaviour sometimes, maybe just paranoid.

So far: I assume a 1ton HX will do fine outside, but read some papers saying enlarging the HX and running refrigerant at slower speeds inside it is better. I presume I should not go lower than 1 ton, but higher is ok ? I'm trying to source HX's but without luck here, a shell-tube HX would be nice, or making my own (blindly dimensioning it).
https://dl.dropboxusercontent.com/u/...2014.23.19.jpg
https://dl.dropboxusercontent.com/u/...2014.26.23.jpg

So, opinions, ideas, do's, don'ts, part sourcing ?
Cheers,
F

Wow I like that !

how many watts does it use, I assume you are using 110v x that by the amps and you will get the watts.
To find your Btu's rating - Find the seer value then compare its electrical consumption to other units with the same seer rating.

Hi, Europe is 220V, there is some consumption data posted in "Statistics". In the lowest compressor speed it takes 160W, with compressor off and only fans running unit takes about 40-50 watts. I've seen the compressor ramping up to about 1300w in my case, but not more for the moment, wasn't very cold yet.

Is it one of these units?

Midea Heat Pumps, New Zealand

Model number or numbers? I have come not to trust the claims of the off-brands, as well as many of the name brands. This Chinese company brags up their own name even before starting on the heat pump units.

Jeff, none of those, it is one step smaller, 07 (from 7000btu in cooling), but physically it appears to be a 1 ton unit, with different software, maybe different EXV, but the size of the HX looks to be identical to the 1 ton units. It is called something like MSX07HFNR or something like that. I studied similar units with the same compressor, they are branded by a large number of brands, including Toshiba I think. The 09 and 12 models have lower COP, but this rare unit with 1 ton guts says it has 5.56 in heating. Inside it looks to have same guts as premium units, including Chinese components, identical to those found in Toshibas, Sanyos, Mitsus etc. I cannot measure the real COP, but even if not 5.56 it is pretty high. Before it, a resistance heater labeled 1.5kw wasn't able to deliver any kind of comfort, the pump is a world of a difference with about 300W/hr or less.

It looks to me like what you have is a "mix-and-match" unit. Much like the automotive industry, the mfr's have made these mini-split units interchangeable. Terms such as "platform" and "brand badging" come to mind. Many different brands and models come from essentially a very few compatible units. The main differences are cosmetic, such as stickers and plastic bezels. Nearly everything is made this way nowadays; it's a product of lean manufacturing processes.

A good property of these kinds of units is that they are very robust. The digital controls these systems use are pretty much self-regulating. No matter what modules you rig together, they will all work with each other and do a good job of it. With your unit, the controller learns rather quickly that it has a small indoor unit hooked up to it and behaves accordingly, running at reduced power levels most of the time. The energy efficiency of this mode is stellar.

Looking at service manuals of a few of the various midea models, it seems to me that running the outdoor unit as a water-source unit will be challenging. It will be less of an exercise in plumbing than of fooling the digital controls. The outdoor unit was designed as an air-source unit, and has all kinds of sensors in it. The fan is brushless DC, and has a tach built into it like a computer fan. Depending on the model, the units have 3 or more temp sensors embedded to tell the controller about its environment. Outdoor ambient temp, compressor discharge temp, hx discharge temp (maybe air and refrigerant) are all monitored.

Here are some of the more useful manuals I found. Not knowing indoor or outdoor units' specific model numbers doesn't hurt my feelings. The x-series literature is somewhat of a contradiction in itself, stating super-3d-hd-dc-inverter compressor yet showing cap tubes in outdoor units...

http://midea-poland.pl/_media/dok_te...HRFN1-QE4B.pdf

http://e-klimatyzacja.pl/instrukcje/...ICE_MANUAL.pdf

Jeff, I don't believe the fan or the sensors are too much trouble. The temperature variation here as air vs water is not much in mild winters ( actually in mild winters Danube is a little bit colder than the air sometimes). I'm planning to use the actual fan controls to power up a brushless dc water pump, from my initial investigation, voltage and rpm wise it seems to match, although I would rather have a faster pump to avoid freezing up the hx.

The trick is to control hx freezing or even to use the current controls to heat up a very cold HX, and again I don't think this is too tricky, maybe I'm ignorant. What I can be sure is that the unit will think the hx is frozen more often in an WSHP config, but I have seen people tweaking the temp sensor for allowing colder temps in the hx without going into defrost mode. It seems the unit does defrost in 2 ways, first it reverses flow of refrig., secondly there is a heat strip in the pan to clear ice from the pan. I can use the heat strip strapped to a hx to heat it up. Also - defrost only seems to happen when frost reaches the top sensors on the hx - you can see it in the photo. Tweaking the defrost seems doable to me.

Question: does anyone see a problem with using a very large suction line HX as the actual outdoor water to refrig. HX? The problem I see is refrigerant flow minimum speed to be reached to carry oil back. Anything else ?

aquario just posted up a new offering from Danfoss: the digital compressor package. The components of this "roll your own" package are very similar to what you have.

check it out:

http://www.ra.danfoss.com/TechnicalI....019.A2.22.pdf

The diagram on page 2 is almost what you have in your heat pump. Just subtract the eev and check valve from the indoor unit, and substitute the danfoss controls for generic "midea" parts. This "house that Jack built" approach is spreading across the world as we know it.

Jeff, I am familiar with the "platform" production concept and I believe this is going on in HVAC for many years. I assume my platform is some generic Chinese package under Toshiba specs, sold as various brands around the world, as you said. I read some papers from Toshiba and Mitsubishi about how they design compressors, it looks like almost all compressors are manufactured by a handful of companies in the world, under the designer specs. My compressor is listed as a Toshiba compressor in some papers and spec sheets and most of the info comes from the actual manufacturer GMMC or something like that. Anyway - guts aside, let's focus more on the hacking. Any ideas about the HX question I had before ? I'm also considering stripping all the fins from my outdoor air coil, make it a bit more compact and encapsulate it in some sort of box or tube and run water through it. Probably cheapest option and maybe no brazing involved.

Ooh, I don't know, man. That sounds like a waste of a good heat exchanger to me. Once you do something like that, there's no going back. Not to mention any warranty you might have.

If you're considering something of that nature, consider enclosing one side of the outdoor HX with a shell, like an auto radiator. Water conducts lots more heat than air, so you don't need very much surface area to do the job. The bends and u-turns that contain the refrigerant would gain or lose heat (depending on operating mode) to the river water just fine. Since the river water would be under very low pressure, you might get away with sealing the end with silicone and clear plastic or pond liner material.

During cooling season, I know for a fact you can just feed cool water into the drain pan to submerge the bottom inch of HX. This alone will boost the capacity and efficiency of the outdoor HX A LOT. Those half a dozen passes or so of piping at the bottom are enough to lower condensing temperature 20-30 degF. The hotter it gets in the summer, the better that little bit of water will boost your efficiency.

Both of these suggestions make no major material mods to the outdoor unit. To resume original operation, you just quit pumping water and let it drain out. Your warranty stays intact and you can easily remove the mods for a unit swap or factory repairs.

Jeff, not sure if I was clear enough :-) The hack has to happen so warranty is no issue anymore. I'd love to have this thing kept intact, but there is no way I'll be sailing with that thing on my deck, so needs to go below decks, hence the hack. I did a rough estimation of the current outside HX line length. There are 3 circuits in parallel in the HX totaling about 51m of pipe, pipe seems to be around 7-8mm OD.
An idea would be to make my own HX based on that pipe length, 3 coils of 8mm Cu tube inside black PEX or HDPE pipe in parallel, each coil 17m of pipe length. Could stack them all in a bucket with the compressor and other guts inside the bucket and be done with it. Now, writing about it, seems very doable and easy. It would be damn nice to have a shiny of the shelf shell in tube HX though...

Here are some of the coax exchangers you speak of... Turbotec brand:
http://www.boreal-geothermal.ca/imag...elixspec21.gif
http://www.boreal-geothermal.ca/imag...ec_table11.png
smaller
http://www.boreal-geothermal.ca/imag...ralspecs21.gif
http://www.boreal-geothermal.ca/imag...ec_table21.png
larger

In the USA, these coax coils can be found on ebay or at surplus city liquidators. Your mileage may vary in Europe.

Surplus City Liquidators

Yeah, those would be nice. I contacted them about shipping one of those over here, they only want to ship with UPS which was ridiculous in price. USPS would be 4 times cheaper. Interestingly almost all HX from turbotec are rated 450psi, which is too little for R410a, however, I found that they have updated product codes for some of them and with the updated code they are rated for R410a, I suspect it is the same product, but who knows.

I also learned that a 1ton HX is not a 1 ton HX everywhere and in every application. They are rated for a certain evaporating/condensing temperature and most of them don't mention the temperature they are rated for. Basically if you need to suck heat from -20deg C outside air your HX, even if in 1 ton is huge and probably equivalent to a much higher tonnage for warmer temps. Given this, if I will have a change, I will go much higher than 1 ton.

More poking inside the outdoor unit. Found a little metal encased box at the bottom of the unit. After checking several other manuals from other units, I now presume it is a so called 'reactor'. What exactly is it and what is it doing ? Anyone knows ?

If they turn out to be what you need you can have it shipped to me in the states. When I get we can mail it out to you USPS you can just paypal me actual shipping. We ship six days a week we will just add it with the other we stuff we ship.

Any updates on this BeerGrylls?

That's the boost inductor for the active PFC.

spring is coming
 

Hi All,
Firstly, many thanks pinballooking for the offer. Unfortunately I haven't found a suitable HX yet. If I do find one in the states I would definitely appreciate some help with shipping. Secondly, there is no progress except doing lots of reading and searching for HXs. This is a high pressure unit and there aren't any HX I can afford around this corner of the world, or other places. I am also studying the design of this pump and others as well, to see why and how they are built they way they are.
Thirdly, what is a boost inductor for the active pfc in laymen terms ?
Last night I pulled the entire indoor unit apart due to noise and vibration, was trying to rip itself off the bulkhead. I found out: the centrifugal blower end support it is really bad design, and those little Chinese children assembling the unit forgot to add grease in this rubber end sleeve suporting the blower on one end. Now it is packed with grease and running smoothly, at least for some time...
Since there is no HX in sight, I have been thinking of stripping all the alu fins off the outdoor hx, unfold it flat ( it us L shaped now) and put it in a black box with a perspex or acrylic glass screen and mount it on the boat transom. When real warm weather comes I will first evacuate the unit and start chopping it up. I am really afraiud of how much a company will quote me for the gas recovery, been thinking better find a recovery machine on ebay, do my work with it and sell it again...
Anyway, this is as much info I have for the moment. Been really happy with the unit so far. About 7.8kw/day average. We had about 2 weeks of -10 degrees, ice around the boat, but not touching the hull. Boat was warming the water around it.
Another hx alternative I have been thinking about - buy a used cheap big indoor unit, strip the hx as it is compact and put it in some sort of casing.
Cheers from the warm boat.
F

Btw I have looked at the size of the current hx for referrence, if anyone interested.
Outdoor about 51 lenghts of 76cm pipes, 3 circuits, pipe is 7.6? mm weird diameter, probably not metric.
Indoor 36 lenghts of 70cm pipes , same od, 4 circuits.

So indoor hx is roughly 2/3 of outdoor hx.
Cheers
F

I found a grossly oversized Hx here:

copper refrigerant pipe: $113
TURBOTEC | COILS, STEAM & WATER | 3-1/2 TON COAX COIL | Surplus City Liquidators

cupronickel refrigerant pipe: $208
TURBOTEC | COILS, STEAM & WATER | 4 TON COAX COIL | Surplus City Liquidators

Both are rated at 450 PSI working pressure (burst pressure much higher). Your water-source setup should run at much lower working pressure in cooling mode (450 PSI = 125 degF saturation temp, 100 degF Tsat = 317 PSI). In heating mode, pressure is not an issue (freeze-up is related to pump sizing).

OR

You could look into China and have one custom built for cheap. Some suppliers will pretty much design and build a single one-off part for you, given pertinent performance specs. Not very expensive, either.

http://www.alibaba.com/product-gs/15...Exchanger.html

Thanks Jeff,
I've been looking at those before, but, with shipping and tax they end up half what I paid for my heat pump. Looking for a more budget friendly option. Secondly, I understand that a grossly oversized single hx will destroy my precious compressor due to low speed/flow of R410a. I read that there are minimum flow rates for 410 due to lubrication issues. This is why my hx has 3 circuits with thin lines among other things. Can anybody comment on the minimum flow rate ? At least this is what I read and I am trying to avoid lubrication problems.

Indeed it looks like the Chinese market is a good candidate even price wise, some offer this hx with free shipping:
Aliexpress.com : Buy free shipping fish piano music game carpet Fashion Children's Educational Toys fish Music crawling mat, baby toys blanket from Reliable carpet stair suppliers on Ningbo Haishu Chosen Trade Co., Ltd.
Not sure if the specs are ok. Will keep looking.
If oversized, I understand it is better to have several smaller hxs in parallel due to min flow rate required for 410a.
Cheers,
F

Oil carrying problems are unlikely in a condenser due to liquid refrigerant being a good solvent. You can add a little R290 (refrigeration grade propane) to act as an oil carrier.

Many thanks for the input Mike. It is good know, however what if the coil becomes an evaporator ? I actually try to refrain from using those designations since they switch around. My outside hx will also be used for cooling/dehumidifying, therefore there will be gas flowing through it too, not just liquid. Should I still be concerned ?

The multiple paths and thin lines are a method used in r410 units because they can tolerate more pressure drop in the lines. Since the high side is so high pressure, the smaller lines do not hinder flow like in r22 systems. By using more smaller lines, the mfr's can maximize the surface area of active piping.

How do you know that this is true?

-AC

One of those Purdue research papers. I commented on and maybe cited the article in a past thread somewhere. It had to do with micro-tiny, rifled tube construction and performance optimizing specifically for r410a. I had commented "How will I hack a heat exchanger made out of cap tubes?"

I found some literature in a hurry: Micro-groove

main page

specific paper
http://www.microgroove.net/sites/def...6755_final.pdf

If I may expand somewhat on Jeff's comments:

R410A has roughly 40% greater saturation vapor density than R22. The higher working pressures allow smaller cross section in the same sense that high voltage lines permit smaller wire cross section.

This has multiple benefits. Smaller tubing has lower hoop stress for a given pressure, allowing for thinner walls. Thinner walls increase heat transfer and lower cost. More tubes in a given HX area further increase heat transfer. Higher fluid velocity also increases heat transfer.

R410A gets a bad rap because it doesn't work in old equipment. Systems designed for R410A can outperform R22 and R290.

Ref. " Effects of refrigerant properties on refrigerant performance" Prapainop and Suen. 2012

I'm still having trouble with this notion. I just don't see how higher pressure equates to lower friction ("the smaller lines do not hinder flow like in r22 systems").

The electrical metaphor isn't doing it for me either.

The rest makes perfect sense.

A well-thought response.

I tried to find a copy of the Prapainop and Suen paper you mentioned, but none of the links I tried were live.

Do you have a working link to the paper?

-AC

how about a water analogy? If you only have 20 psi of water pressure, you're going to need much larger supply pipes to feed the same gpm than if you had 50 psi of water pressure.

Yes, the laws of physics still apply, but with R410a, the increased pressure and corresponding gas density lends itself to smaller hx size and tube diameter at the same exchange capacity. Obviously, this effect is much more prevalent in the condenser side.

Thanks for posting this very useful paper.

I did look at the authors and it gave me pause, as the world of HVAC was "ruled" by US businesses after WW2 and now the crown has been clearly passed to Asia.

Great info in this paper though, it will greatly inform our discussions.

Thanks.

-AC

I think that your comparison breaks down because the water analogy assumes pressure at one end of a pipe, and no pressure at the other end.

In the refrigeration circuit, all events take place within a hermetically sealed 'world', thus the pressure is balanced. Refrigerant flow is caused by the "unbalancing of pressure" due to the work of the compressor.

-AC

The US may still dominate the business world but research left our shores more than 30 years ago. I was a member of the Society of Automotive Engineers in the 80's and 90's. By then nearly all the SAE papers were coming out of Japan.

Ok, lets get detaily.

In a typical R22 unit, we have 70 psig low side and 225 psig high side pressures. In a R410a unit, these pressures are 120 psig and 350 psig respectively. So we have twice as much pressure, nearly. R410a therefore has nearly twice as much gas per unit of volume compared to R22. This helps the heat capacity a lot. So much that it throws everything off balance by 40%. You need either 40% less compressor or 40% more heat exchanger to balance the load.

With home- or mini-split-sized heat pumps, the trend has been to add 40% more heat exchanger. A previously 1 ton sized compressor has now been spec'd to 1.5 tons for R410a use, and that part was easy. The heat exchangers have been altered to have more capacity per square inch of face area by doing what? Instead of a hx that has 3 circuits of 3/8 inch pipe in them, they now have 6 circuits of 3/16 inch pipe in them. The pipes are also stacked closer together.

The result is just like a new 1.5L vtech motor that has more horsepower than an old 2.8L slant six motor used to. The new breed of heat exchangers have much lower internal volumes, less weight, and higher flow rates than the old ones did. Guess what? Noone cares that they have 15% more pressure drop. The R410a works anyways. Less refrigerant charge, less copper, less weight, more capacity. TADA!

R410a is a 50/50 mix of R32 and R125. R32 makes a great refrigerant (competitive with R290), but R125 isn't particularly good. Look it up and you'll find that R125 has a high GWP. As it turns out, it was really put in so the fluorocarbon companies would have an excuse to phase it out when the patents expire!