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BeerGrylls 01-11-14 06:17 PM

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).

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

ecomodded 01-11-14 06:40 PM

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.

BeerGrylls 01-12-14 04:41 AM

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.

jeff5may 01-12-14 10:45 AM

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.

BeerGrylls 01-12-14 11:14 AM

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.

jeff5may 01-12-14 04:17 PM

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.

jeff5may 01-12-14 04:37 PM

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...

BeerGrylls 01-12-14 04:46 PM

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 ?

jeff5may 01-13-14 05:36 PM

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:

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.

BeerGrylls 01-14-14 12:05 PM

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.

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