Help design my new system please

[buffalobillpatrick]

dhaslam, that makes me think that I could use a TMV (thermostatic mixing valve) to limit the upper temperature from the solar tank into the evaporator, Thanks.

[NiHaoMike]

A custom build can go higher than that. The issue is overloading the compressor due to excessive suction pressure, which a R410a compressor will handle better. The issue of discharge pressure going excessive is avoided with an oversized condenser. The compressor would actually run cooler due to a lower compression ratio and higher mass flow rate.

You can throttle the flow to limit evaporating temperature, but it's more efficient to slow down the pump. And even more efficient to design the system such that it rarely need to throttle. Using a R410a compressor with R290 gets you a good part of the way, and using a VFD may let you dispense with the throttling altogether.

The heat exchangers you selected are good. You'll probably want a suction accumulator since that form of heat exchanger has less internal volume so getting the correct charge is more difficult. You'll also want an oversized liquid line filter drier to act as a liquid line receiver.

[jeff5may]

Or you could put in a "quiggle-ator" aka refrigerant charge compensator. Since you are considering such a wide temp range to source and sink heat in your proposed design, it makes sense to vary the charge. Basically, it is an expansion tank wrapped around the suction line, between the outdoor heat exchanger and the reversing valve (or compressor suction accumulator).

Since you have spec-d between 35 degF and 120+ degF temps for your thermal store, and plan on boosting this temp to DHW range if necessary, a simple suction accumulator or liquid line receiverr would have to hold nearly all of the system charge. Either one could go haywire if sized too small and pushed hard one way or the other. The compensator basically maintains a near constant charge in the condenser hx regardless of what the temperature range is.

If the temperature of the evaporator is low, the overall system pressure will be lower. The charge compensator will condense out some gas to keep the hx's from flooding. When the evaporator temp is high, the overall system pressure will increase. The compensator then boils off some liquid inside itself, forcing more refrigerant back into the system.

I have attached a basic training brief on the things. Another good illustration is in this pdf:

http://www.hvacpartsshop.com/HP25%20Series.pdf

Page 4 has a sliced-open view of the outdoor unit. The illustration on page 11 (fig. 17) makes it easy to see what the thing actually does. As with anything, if you ask three engineers if it's useful, at least one of them is going to say no. But the things do work and don't break in strange ways.

[NiHaoMike]

No need for a charge compensator (expansion tank) since it's a one way heat pump. And when one is used, the cap tube should be connected to the bottom so any trapped oil can escape.

The liquid line receiver (or an oversized filter drier that also works as one) will take care of maintaining 100% liquid to the TXV without backing up too much refrigerant into the condenser. Adding a sight glass can help with getting the correct charge, but beware that some mixtures like R433b will appear to bubble slightly when properly charged. There should be no big bubbles when properly charged, but small bubbles might be OK depending on the refrigerant.

The heat exchangers should be mounted such that the liquid connection is at the bottom and the vapor connection at the top, with the water flow opposite refrigerant flow.

[buffalobillpatrick]

I have been searching all day for a quality reasonably priced VFD
Most of them look like cheap krap.

[NiHaoMike]

You'll do better buying a used one that still works. Even then, it might not be worth the cost.

Have you finalized how much capacity you actually need? That would be especially important without a VFD, but a VFD is not a substitute for rightsizing. Once you have that down and whether or not you're planning to use a VFD, part selection for the rest of the system can begin.

Save on A/C and Heatpump bills using used VFDs Part 1 - YouTube

Save on A/C and Heatpump bills using used VFDs Part 2 - YouTube

You'll also want to look into ECM pump motors.

[buffalobillpatrick]

Yes I watched those earlier today, Is that you?

Size needed is a good question?
About 2.5 tons as I think that is 30Kbtus which is my design heating load.
Only need that much about 4 nights per winter, but for a real long cold snap below 0* F ?

The best prices that I can find on compressors is at Surplus City.
I dont know what to choose:

The Danfoss is made in USA weighs 68#
MITSUBISHI is made in THAILAND weighs 82# I'm unsure about it's VOLT:220/240, HERTZ:50

Price per pound, Mitsubishi wins. hehe

??????

Danfoss $169 + S&H
2-1/2 TON AC/HP SCROLL COMPRESSOR, VOLT:208/230, HERTZ:60, PHASE:1, LRA:96.7, CAPACITOR:45 X 370(NOT INCLUDED), REFRIGERANT:R-410A, CONNECTION SIZE:1/2" X 3/4" SWEAT, HEIGHT:16", BASE DIMS:7-1/2" X 7-1/2", WEIGHT:68 LBS, ORIGIN:USA

OR

MITSUBISHI $123 + S&H
2-3/4 TON SCROLL COMPRESSOR, COMPATIBILITY:AC/HP, VOLT:220/240, HERTZ:50, PHASE:1, LRA:?, REFRIGERANT:R410, LINE CONNECTION:1/2" X 3/4"SWEAT, BASE DIMS:7-1/2" X 7-1/2", HEIGHT:17-1/2", WEIGHT:82 LBS, MADE IN THAILAND, ***NO ACCESSORY***

I think I can make a 240vac soft start with an Arduino interrupt sketch that I have working, power Triacs, zero cross detector, etc.

BBP

[NiHaoMike]

That's another young HVAC engineer out there. For your reference, I prefer to custom build electronics, especially the stuff that's easy to build. I would have used a prebuilt VFD if I could find one cheap and/or needed to get it up and running soon, but I would have built my own temperature controller. That analog controller (don't let the digital display fool you) probably just uses a few opamps to implement PID. (And I'm Chinese, as you might be able to tell from my username. Which basically means "Hi Mike!" and that's what others would often say when I joined meetings at the Texas A&M science fiction club.)

The Mitsubishi weighs more because it's 50Hz, so the actual compressor has to be bigger for the same tonnage. It's going to have lower suction and discharge pressure limits when run at 60Hz. That's still going to be more than we need so the Mitsubishi should be just fine. You'll have to track down what run cap it uses, and pick a 440V version as it would be more reliable. EDIT: the cap you want is going to be about 5/6 the listed value (round to nearest standard value) for 50Hz, because a capacitor has lower impedance at higher frequency.

Here's a TXV that would work nicely:
RHEEM | TXVS & METERING DEVICES | 2.5 TON EXPANSION VALVE KIT | Surplus City Liquidators
At that price, you might as well pick up a spare or two.

Here's a filter drier that would double as a liquid line receiver:
EMERSON | DRIERS,STRAINERS,MUFFLERS | 3/8" FLARE LIQUID LINE FILTER DRIER | Surplus City Liquidators
Be sure to install it with the outlet facing down and do not open it until you're ready to put it in and pull a vacuum.

Here's an accumulator:
PARKER | RECEIVERS & ACCUMULATORS | 3/4" SWEAT SUCTION LINE ACCUMULATOR | Surplus City Liquidators

Add those to the other parts you listed, plus a set of service valves and some tubing and there's your heat pump. If you put it together before you're ready to run it, you could pull a vacuum and then put in a "holding charge" of 100 PSI or so of either refrigerant or nitrogen.

You can't soft start a compressor with a triac. Given that it's a scroll and you're running it on R290, it most likely won't need any help starting. Just switch it with a contactor and call it done.

EDIT: There are also a few more "optional" bits (that are not required to make a working heat pump but are a good idea) like the high/low pressure cutouts and the sight glass to choose, so don't order yet.

[buffalobillpatrick]

NiHaoMike, Sorry about my disparaging comment, I'm rather a coarse fellow & frequently step in doo-doo.

Thanks for the parts list, the 50hz Mitsubishi wont be an issue? At 60hz wont it run faster & heat up more? Possibly put out >3 Tons?

what does this mean? "It's going to have lower suction and discharge pressure limits when run at 60Hz"

I plan to use the Thermal Accumulator's aqustat to control heat pump. If Solar tank is > 35* F.
Aqustat set with 20* delta should run heat pump for about 40 min.
(120 x 20 x 8.3) = 19,920 btu…………. (19,920 / 30,000) x 60 = 39.84 min.

I have read that PAO oil is the right stuff with R290, how to determine how much to put in system?

What type of copper pipe? Are flare fittings ok or should be avoided? Are the ports a special type of schradder valve?

I think I see 7 places on the loop to put temp. sensors, including one on the middle side of each HX? I can monitor these with Arduino. I think I see the need for 4 pressure gauges?

BBP

[NiHaoMike]

It will run faster, but then you're using R290 so it would not overload. If anything, it would probably end up matching better to your application. It just means that it won't be able to work at as high a pressure as a 60Hz R410a compressor, but that's still more than enough for our application.

Here's a low pressure control:
HONEYWELL | CONTROLS PRESSURE | HONEYWELL LOW PRESS. CONTROL | Surplus City Liquidators
It says non adjustable, but you'll see a gear in the side that lets you adjust it by prying it back and forth with a screwdriver. You'll probably also want to use a screwdriver to "click" the switch a few times (insert between the diaphragm assembly and switch and apply pressure to the rod coming out of the switch) to make sure the contacts are clean. To set the pressure, once you have put together the system and pulled a vacuum, put in a holding charge at the pressure you want it set at, adjust the switch until it turns on (if needed), then adjust it until it just turns off.

Here's a high pressure control:
HONEYWELL | CONTROLS PRESSURE | 425# HIGH PRESSURE CONTROL | Surplus City Liquidators
The default 425 PSI setting should be fine since it is intended to prevent catastrophic system failure.

Here's a sight glass:
ALCO | MOISTURE INDICATOR/SIGHT GLASS | 1/2" SWEAT MOISTURE LIQUID INDICATOR SIGHT GLASS | Surplus City Liquidators

Here's a contactor:
CONTACTOR | CONTACTORS & STARTERS | 2 POLE 40 AMP CONTACTOR 24 VOLT COIL | Surplus City Liquidators
Get several to you'll have spares and in order to control other stuff as well.

Here's a 24V control transformer:
BASLER | TRANSFORMERS | 40 VA 208-240 VOLT PRIMARY 24 VOLT SECONDARY TRANSFORMER | Surplus City Liquidators
Get a spare or two. It's cheap. You'll want a 2A or so slow blow fuse for the secondary, commonly available at electronics stores.

I looked up the compressor and it specs a 50uF cap. For 60Hz, that's about 42uF.
CAP RUN | CAPACITORS | 35+7.5 MFD X 440 VOLT OVAL AC DUAL RUN CAPACITOR | Surplus City Liquidators
Again, for small, cheap parts, a few spares are a good idea. Parallel both sides to get the correct capacitance.