Inverter Ac converting into air-water heat pump
 

My current setup is an 24000btu R22 external unit.
This is heating my 1000L plastic tank once a day, which is insulated with 10cm of extruded polystyrene. Inside the tank I have 10mm copper tube/ 20m for heat transfer.
To have the best efficiency I programmed to start the pump once at 2PM when the outside temperature is the highest.

In the summer 20min of running heating the tank for 24 hours need.
In the winter if the temperature is dropping to 5degC it runing 1, 5 to 2 hours. Under 5 C I need to heat with an electric heater.

Now I want to improve something and extend it to house heating too, not just hot water.

I want to change the external unit with an inverter one.
The idea is simple, not so simple to do it.

I have 2 options:
1. Buy a new heat pump - no fun, spending lot of money
2. Converting an inverter AC unit - lot of chalanges, price is almost 10th of the new one + time spent for fine tuning. I have this idea from long time ago.

I have some knolege about automations, so I can jump in.
My passive house need is 5kW thermal heat, I guess one 18k unit will be fine. This thread can be used for bigger needs.

The chalange:
1. Install the external unit- easy
2. Connect the coil or one heat exchanger to the unit - easy. I prefer heat exchanger.
3. Controller setup
A. Use the indoor PCB and find a way how to cheat to have the needed control of the outside unit
B. Learn how to send specific command to the outdoor unit and build a simple arm based controller
C. Maybe sombody did it an I don't know
D. Buy a ready-made controller with 0-10V input - tried to search but hard to choose

Now I'm writing from the phone, I will put pictures of actual setup later. I will have more updates.

Have a nice day
Ferox

What do you want to achieve when you said that you want to control the outside unit of the inverter ac ? Do you want to control the indoor temperature , keep a fixed flow temperature , or what ? As you see from the pictures , I'm using a 24k btu inverter unit to heat my house of 126 sqm , located in Buzau , Romania . Is your house located in Oradea ? Good luck with your project !

Ps : on my computer the pictures look fine , they don't need to be rotated . I don't know why they've been attached this way and I don't see the option on ecorenovator to rotate them so they look normal .

https://ecorenovator.org/forum/attac...4&d=1603615489

https://ecorenovator.org/forum/attac...5&d=1603615489

Hi Sadashi!
Yo have a nice setup, you did it! Exactly as I want to do it.
My goal is to control the power of the outside unit, than I can keep a fixed flow temperature.
Can you share with us how you control the water temperature? In that case I don't need to reinvent the wheel. I have some ideas but always it is a risk that is not working as intended.
My 140sqm house is located in Oradea, where the weather is not so extreme as in the rest of the country.

Best Regards,
Ferox

Some pictures from the old inefficient setup.
External unit was modified to be able to have cooling for defrost proposes connected directly to the coil which is in the bottom of the tank. Was installed 7 years ago, working good, controlled with Arduino and Blynk app for remote control and visualizing the temperatures with the nice charts.
The plan is to upgrade with the latest inverter technology for heating the house.

https://ecorenovator.org/forum/attac...6&d=1603636625

https://ecorenovator.org/forum/attac...7&d=1603636791

https://ecorenovator.org/forum/attac...8&d=1603636791

https://ecorenovator.org/forum/attac...9&d=1603636791

https://ecorenovator.org/forum/attac...0&d=1603636791

https://ecorenovator.org/forum/attac...1&d=1603636791

Inverter control
 

I'm afraid that I will disapoint you with regards to controlling the inverter unit to be able to keep a certain flow temperature . I'm not saying that it's not possible , but for me it wasn't a must , as my system the way it's been setup ( with radiators ) doesn't required a certain temperature , it varies depending on the indoor temperature . The inverter unit modulates the power output to meet the set temperature that I'm asking from it , so the flow temperature varies .

I understand. You are using the original controller.
Is the easiest way of doing, just instead of internal air heat exchanger is an water HX.
In the same way I can put the temperature sensor of the air to the floor heating, in that case I can go just with temperature lower than 30degC.
Maybe I can find a way to cheat the room thermistor input.
How many sensors has your internal board, did you connected to HX?

Indoor sensor .
 

If you have underfloor heating , then you can put the indoor air sensor on the return flow pipe and set your indoor temperature to 30°C from the remote control , this way if delta T is 5°C between supply and return , then you should have 35°C on the flow pipe . I have only one thermistor on the brazzed plate heat exchanger .

Water temp
 

I've been thinking of using a similar system for my underfloor heating. Can either of you tell me how high a temperature can you heat the water? I need to add 15K BTU and I need to heat water to 125F. Is that possible?

BTW nice job on that coil.

It is possible
 

I have a dhw tank of 300 litres , and the water temperature can reach at the top of the water tank 140°F ( 60°C ) , so it is possible to obtain that temperature , but it is limited on the volume of water that you have in your underfloor heating . It depends where is your house located , if the winters are not that harsh and there isn't a high humidity area when the outdoor temperatures varies between 40°F and 25°F ( it defrosts more often ) , then you should be ok .

Based on options that I have, I choose option 1 is more likely for me
Option 1 : buy new heat pump Mitsubishi 7,5kw, 5kW not available.
- eazy installation
- if I want to sell the house is better
- service friendly, not need my assistance

Option 2:
- finding the right unit is not easy
- hi COP unit rented to 5 is expensive
- lot of chalanges
- warranty lost

Option 3:
- gas boiler is half price of heat pump
- gas price is more volatile than electric
- cannot be used with PV panels
- yearly authorized person verification needed

Sadashi,
As I understand, you use the original controller of the inverter airco. You have placed the temperature sensor from the indoor coil on yhe brazed plate heat exchanger, and the air temp sensor on the water return.
But what did you do with the fan of the indoor unit? Did the original controller not complaint when you run the ac without an indoor fan connected?
Love to hear more details on this setup,
Murdock

Sensor position
 

Hi Murdock and welcome to the discussion . There are two sensors with this C&H ( Gree made ) unit that I'm using , one was attached to the copper heat exchanger ( evaporator ) and the other one is the air sensor . The one that was attached to the evaporator I've placed it on the refrigerant liquid line right after is coming out of the brazzed plate heat exchanger and the air temperature sensor I've extended the wire and I've placed it somewhere inside the house on a wall along with the small led display that's got the ir receiver as well incorporated . You have to keep all the electronics of the indoor unit and also the fan motor to be able to control the outdoor unit . You detach the fan motor from the fan and place it somewhere in a box and secure it somehow so it won't move when it starts spinning . I haven't tried to trick the pcb and not keep the motor because I believe the motor got a sensor on the inside that communicates with the pcb and if it detects that the motor does less than 450 rpm it will shut down the unit .

If you investigate the motor a bit more you'll probably find one of the wires is providing a square wave pulse output that varies depending on the speed of the motor.

It should be fairly simple to build a circuit (i.e. 555 timer) to simulate this output and allowing you to dispense with your 'motor in a box'.

Agree with Acuario. It can be relative easily hacked. On the orher hand, I guesse the motor spinning without any load, will probably comsume ony a few watts. All in all, Sadashi, it looks quite easy to modify the airco to an air-water heat pump. Have you got an idea about your COP? Since you haven't altered anything of the outdoor unit, I would assume you 'll have a COP close to factory spec.

I see a few fundamental misconceptions with your project. Just going to ask a few questions to clear up the mystery.

So the system you have running is a constant output unit that you have running full blast for a short time to satisfy a whole day's demand? And you plan to substitute this unit for a variable speed unit of similar capacity? You may pick up a fair amount of efficiency, but at what cost? A finance payment on a new outdoor unit will probably equal the existing unit's electric bill.

If your existing unit has capillary tube metering, you may be able to increase its efficiency at a pretty low cost. There are a few ways to accomplish this. Which way to go depends a lot on the existing unit, as well as your skill set and confidence level.

I'm assuming this system is your primary home heating. Of so, and you don't have sufficient backup heat, a diy solution might not be the best idea. These things tend to fail during the most extreme conditions when you need them the most.

I need to change my system based on two factors.
1. Old unit is not running well under 5degC.
2. Old setup is heating just the water tank, once at the highest temp of the day. House heating is a small wood stove, if I'm not at home is expensive to heat the house with electric radiators.

You are right, the system will fail when you needed most.
My backup remain the wood stove, even if the system will fail the house is very well insulated, loosing 1-2 degree C in one day, depending of outside temperature and sun.

I chose to buy one of the shelf heat pump, but until I save money fot this I can made a cheeper plan.
For the cheeper plan can anybody recommend a system type with high COP? And made it like Sadashi did.

It's more than just high COP in my opinion . You can have high COP at A7/W35 but the unit will loose heating capacity dramatically when the cold weather is coming and you need it most . I would choose a Japanese manufacturer but not Daikin ( it loses about 40-50 % heating capacity at negative temperatures ) and not entry level units . In my opinion is more important to have heating capacity at low temperatures with lower COP , than high COP at positive temperatures and no heating capacity at low temperatures , you need to find a balance between them two and you need to find out how many kW of heating does your house need when you have -15°C , -20°C outside and then look for a unit that can provide those kW of heating at those temperatures . Good luck

If you are looking for a unit to do only slab heating, that makes the system less complicated than one that both heats and cools. If you go with a brazed heat exchanger and a floor slab, you should not need a big water tank. Especially if you are interested in a variable speed compressor unit. That's the big value in using one: no big tank. With a single speed outdoor unit that can dig into the cold temperatures without losing too much capacity, a heat store tank makes a lot more sense.

For domestic hot water heating, there are a few ways to go. You don't need a big heat pump. A few ecorenovators have made heat pump water heaters out of dehumidifiers. Randen made one out of a 5kbtu air conditioner.

Never heard back about your existing unit. If it's got capillary tube metering, you can go with an expansion valve and get better cold climate performance. I just picked up two of them on eBay for about 20 dollars each shipped. What valve to use depends on your unit. Mine will be going into a 2 ton whole house window/wall ac unit that got its face melted in a kitchen accident.