The Homemade Heat Pump Manifesto

[BradC]

Originally Posted by randen

Maybe the little 2 ton may have done the job. A little more refrigerant charge and antifreeze might have done it. Oh well. The joys of hacking.

So as you draw heat from the water, you are unable to keep enough heat feeding the refrigerant to prevent the SST from dropping below the freezing point of water. You have a couple of options. Increase your evaporator surface area and/or water flow rate. Change the freezing point of the water. Prevent your SST from dropping that low.

The third is probably your cheapest option. You have several ways of doing this. They will all reduce the system mass flow. You can slow the compressor, increase condensation temperature or look at an evaporator pressure regulator.

If your compressor will sustain it, an EPR will prevent your evaporation temperature falling below that of the freezing point of water. Do that and you prevent ice buildup. The SST at the compressor will continue to drop until the system mass flow equalizes. Same end result as increasing condensation temperature in that you reduce overall COP, but it will absolutely prevent your evaporator icing up under high load conditions.

You only need the EPR set about 1 degree north of freezing. Ice crystals just won't form if your pipes never drop to or below freezing.

[Vlad]

randen,

When your unit runs in AC mode and evaporator freezes up it means you shifted suction pressure/temperature into too low range. The easiest and right way to bring it back is to increase your discharge pressure/temperature. You have to restrict (lower) water flow on your condenser side and you will see your suction side will go up. Suction pressure regulator or evaporator pressure regulators are bad options. Normally balanced ac can and will run without this "gadgets".

The other option will be to increase water flow on evaporator side, but there is no guarantee that it will not still freeze up.

To slow down compressor is not an option because many compressors will not like it and just die. Also you tried 2 T unit and it was too small. By slowing down compressor you are going back to smaller unit you had before.

When your unit runs in HP mode and your evaporator freezes up you need antifreeze and maybe more flow. But I would start with antifreeze and look if it helps. Just add antifreeze as less as possible. You don't need -20 degree you just need to make sure if you go -5-6 degree ice will not form this is all you need.


If you have plans to use your HP as ac you have to use antifreeze because it is too hard to run ac using water as a medium an keep this water from freezing.

[AC_Hacker]

Randen,

I just found a page with tables that apply to various percentages of Ethylene Glycol.

The tables apply only to ethylene glycol. If you use a different type of antifreeze, you'll need different tables.

The tables describe how various percentages of ethylene glycol will change the freezing point, viscosity, density (actually specific gravity) and specific heat (ability to transfer heat).

These tables don't directly address how changes in percentage of ethylene glycol will translate into changes in required power, etc. but they do illustrate that changes in heat transfer rate and in required pump power will occur.

-AC

[Vlad]

I would go with propylene glycol because it is food safe antifreeze. If leak happens you don't want disaster in your house or even outside. You never know what can leak and where. Also make sure you follow plumbing code. I checked with our city hall they require watts 9d back-flow preventer be installed if you use refrigerant or glycol in contact with water.

Propylene glycol - Wikipedia, the free encyclopedia

It looks like you only need 10-20% of glycole to keep freezing point in -3-7 range

BTW I keep working on my drilling rig. I decided to run it on R290 . My van runs on propane drier, stove, drilling rig, lawnmower.... AC/HP.... what else? It looks like one day I will start eating propane....

I think we should start thread 1000 uses of propane...

[randen]

Vlad & AC_hacker

Thanks for the heads-up. Propylene glycol is the antifreeze of choice I don't need any poison around here. The GSHP is not connected to the water source just a fill line that gets removed. I think I will need protection down to -20 Deg C as the entering & exiting ground loop tubes are exposed on the side of the building. The loop field & the air handler share the same fluid so it will work as well for the AC. Looking at my assembly there is enough room for a little larger evaporator. Knowing that my efficiency will get better with a larger evap. it may be in the cards as well but lets see what the temps are.

Propane seems like such a good universal fuel/ refrigerant. I like the idea, 1000 uses for
R290.

Randen

[Vlad]

Randen,

HP/AC systems are SYSTEMS and require planning when designed. The issue with loop exposed outside is fixable, just insulate it properly. Freezing is an issue but also you don't want to lose valuable loop heat.

I think the number -20 is from nowhere.

I would start from another point. It looks like you plan to use your unit as AC with water(antifreeze) coil. Water is going to be a cooling medium. Here is were you have to start.

1. How big is your water coil?
a. If it is oversized, you don't need low temperature
b. Otherwise you need lower temperature

2. Moisture removal
a. If you need to remove more moisture you need colder coil
b. Otherwise you can stay with warmer coil

3. The lower temperature of your cooling coil the more chance you will have icing. To prevent icing:
a. You need more cfm
b You need warmer coil

As you can see it is more complicated and proper planning must be done before and not after.

Don't put yourself in a box with label "EFFICIENCY". You have many other things to consider. At the end this is your house and not a lab and you need to ask yourself:

"Am I doing this for comfort living or just record high COP (which means nothing sometimes)"

[randen]

Vlad

The ground loop of 4 Ton cap. is buried 6 ft into a clay ground. The 4 ton is about twice the capacity that is required. The header tubes 6 ft deep run up to the building and turn vertically and enter the wall 4 ft above the ground. The tubes are insulated very well with the areo-cell insulation and protected in a big O drainage tube. There would be no appreciable loss of heat in that 4ft. lenght of insulated tube. The problem of freezing may happen when the GSHP is shut down for the weekend or between cycles when its very cold outside. I have seen temps -26 Deg C with lots of wind here. During this winter the temps were quite moderate but I did see one nite of -19 Deg C I kept the circulation pumps running 24/7 even if the GSHP was off to keep the tubes from freezing as I have only water in them. The reason for water only is if I was to work on the system I didn't want to deal with the messy slippery Propylene Glycol. Water is just wet and dries up quickly on the heated floor.

Yes the design was to have AC as well as heat utilizinig a 3.5 Ton 3 speed air handler (recycled) converted for running with water/glcol. Remove the capilleries and install a manifold with larger tubes. The coil is a slant with a condensate tray plumbed to a drain. The air handler seems to work well, supplied with 30 Deg water it returns to the HP at room temp essentially leaving all its heat in the room.

1. You may read in an earlier post I had tried circulating the loop water through the coil to A/C the shop. The result was that the air was cooler and I did remove a lot of humidity but the air was still at 80% R-humid. and a lower air temp but uncomfortable. I need a lower coil temp to wring out as much humidity as possible while lowering the air temp. for the comfort. Ths would involve a coil temp much lower but just above freezing. As you had suggested this may require moderating the loop flow through the condensor or maybe cycling the compressor if the runs time are long enough and not short cycling. And as you have indicated in item 2. and/or increasing the speed of the fan.

Vlad you are right about picking our battles:
"As you can see it is more complicated and proper planning must be done before and not after."

"Don't put yourself in a box with label "EFFICIENCY". You have many other things to consider. At the end this is your house and not a lab and you need to ask yourself:"

"Am I doing this for comfort living or just record high COP (which means nothing sometimes)"

I beleive with this project having built two HP (one 2 T and one 3.5T) that my time spent could have been better applied to my day-time occupation and purchase a comercial HP. But I'm not wired that way. The two units I have built look good and do function however with some tweaking I think they could function as well as the comercial units. My past projects include a 2 seat homebuilt aircraft and it functions far better than a Piper so it can be done.

Now my house is very efficient. Along with the GSHPs and I've just finished installing the last solar hot water collector. We have 9 panels installed 7 that I had built. They work well. With sun we can collect half our space heating requirments.

However maybe you are right. The work involved to build all these things are sometimes not worth the claim: "EFFICIENCY" "Am I doing this for comfort living or just record high COP (which means nothing sometimes)"

My original goals of heating without breaking the bank is being surpassed greatly. I have friends and neighbours who are having troubles affording the oil-man/propane to stay warm. I know its been a lot of work but I'm comfortably warm and I welcome the sun and when I hear the relay click over to solar heating and the knowing this day I won't be paying for heat thats great. The days of wondering HOW WILL I be able to pay this oil bill?? or the one next month?? are just a bad memory.


Randen

[Geo NR Gee]

Originally Posted by randen

Vlad

My original goals of heating without breaking the bank is being surpassed greatly. I have friends and neighbours who are having troubles affording the oil-man/propane to stay warm. I know its been a lot of work but I'm comfortably warm and I welcome the sun and when I hear the relay click over to solar heating and the knowing this day I won't be paying for heat thats great. The days of wondering HOW WILL I be able to pay this oil bill?? or the one next month?? are just a bad memory.


Randen

To me and a lot of consumers, that would make it all worth while! I envy your passion and persistence.

[AC_Hacker]

Originally Posted by Vlad

At the end this is your house and not a lab...

Well, in most cases this is certainly true. In my case, this is not true. My house IS my lab. I directly enjoy the successful fruits of my efforts and suffer the consequences of my failures. It's quite motivating.

Originally Posted by Vlad

...and you need to ask yourself:

"Am I doing this for comfort living or just record high COP (which means nothing sometimes)"

With energy prices rising, as they are and with the economy being as shaky as it is, COP is extraordinarily important.

I sincerely believe that if heat pumps delivered a COP under 100% there would be much less work in the HVAC industry.

With the convergence of rising energy prices and declining economic growth (a convincing argument can be made that rising energy prices are driving declining economic growth) maximizing COP becomes very important.

Randen's stories of the difficult position that people he knows are in, with regards to being able to afford fossil fuel heat bears this out.

Maximizing heating efficiency is much too important to leave to the HVAC industry, or to the scientific establishment.

We have a very important role to play here. Not only are our efforts an inspiration to resourceful individuals in many parts of the world (we only hear about a small percentage of them), but if sufficient DIY momentum is developed, the HVAC industry will be inclined to respond in ways that will benefit the general buying public.

In this way, our documented efforts and successes become a multiple win.

Regards,

-AC_Hacker

[Vlad]

"Am I doing this for comfort living or just record high COP (which means nothing sometimes)"

I do understand and agree that for most of us building an efficient source of heating or cooling is not only for savings in the future. For most of us this is our lifestyle - creating, searching, achieving etc.

My own project went beyond just heating and savings. But I will remind you what HVAC means:

1 Heating our goal is to get not just heating but safe, environmentally friendly, efficient, affordable...

2 Ventilation here is were many of us (including myself) don't pay enough attention. This is our (and not only our) health and comfort. Here are hidden things like moisture removal, air filtration, humidification etc....

3 AC is the other side of the heating coin and in many areas is even more important.

I built very efficient heating system (even using my 65% efficient HWT) in my own house but underestimated ventilation part.

The importance of ventilation in most of the houses is underestimated or completely ignored.
Many people try to cut their heating cooling costs by putting their house inside plastic bag. But try to put the same plastic bag on your head and you will quickly realize that it is not good for you.

So, saying all this I will summarize: when we plan to work on HVAC project we have to consider all letters in this abbreviation (HVAC) and not substitute them with something like COP, EER, SEER, etc. etc.

It looks like most of this EER SEER BS and others are invented just to confuse the public....