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New Zealand DIY Water Source HP.
Hi Everyone,
i finally have my project near completion and currently running in my shed for testing, bring on the winter! I have a small stream that is 60 metres from my house and i use this as my heat source. My stream heat exchanger is stainless steel tube formed into a helix to improve internal turbulence and heat transfer. Evaporator and condenser are coil in shell , titanuim and pvc . All heat exchangers are supplied by vaportec , a company in NZ. It is a water to water heatpump that will be heating infloor radiant slab . I will attach some photos of unit and stream exchanger in a few posts. Cheers Andy |
photo of heat exchanger
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Hopefully photos attached.
The stream heat exchanger is 3 x 6metre lenghts and gives me about 2.2m2 of area and when on full load , if stream is 17 c i will get water returning at 13c , cool it down 2k to 11c and round it goes. The stream stays at or above 10c in winter so a good source that was to good to go past. If you would like any more info ,let me know. Cheers Andy http://ecorenovator.org/forum/attach...140301_001-jpg http://ecorenovator.org/forum/attach...140301_002-jpg http://ecorenovator.org/forum/attach...140301_004-jpg |
how many btu's of capacity are you shooting for?
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According to the performance tables for the compressor at my running conditions , i have 9.5kw on evaporator side and 12.2 on condenser. So 32437btu evap and condenser 41655 btu.
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I know just where you are! Just a stone throw north from Massey University where I have lectured as a visiting professor.
Your climate is quite moderate and with this heating/cooling capacity, you can provide for a large home. A beautiful area if I can say. Steve |
Hi Steve , yes we are 20 kilometers from Palmerston North in friendly Feilding. :)
Yes we do have a mild winter temps with no sustained freezing temperatures , sometimes just overnight. The calculated heatloss at 0c outside and 20c inside is 6kw . The HP is controlled by a VSD so i can adjust output to suit. Cheers Andy |
Welcome to the site Andy!
That looks like a very cool setup. How long have you been working on it? How is the testing going so far? |
Hi DAox , i have been collecting the parts over the last couple of years as we started to plan the house build. The blue steel base and compressor come from an old dairy farm milk cooler, one pump comes from a supermarket sea food case and other from an old radiator heating system and so on.
The VSD had an earth fault and was thrown out , i fixed that and it works great . It gives me alot of information , kw/h , run hours, running amps , running kw, a start delay and a soft start plus of course the variable speed and load output. I have it connected to a high pressure transducer so it runs at 55hz for the start of heating and as it nears setpoint it will slow down to 40hz , this prevents the condenser approach temp from increasing to much and helps efficiency. I must get to work , Thanks Andy |
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This is a really great job you are doing here. We've had other folks who have posted to EcoRenovator, who were considering the possibility of using water flow from a river or stream, but this is the first I have seen of anyone actually carrying through on this plan. Your organization of your mechanicals and your brazing all look really great. So, those three parallel spirals are the actual HX that you will lay in the stream flow, right? And they are made in NZ? Are they being made for the purpose that you are using them for? One thing that I can think of that could give you a problem is that if you have cold winter water flowing through your HXs, and the evaporator is removing heat, which will further drop the temperature, you might encounter a situation where your water flow will reach the freezing point, which would stop flow, and the non-flowing water in the HX could very quickly freeze solid and expand, thus damaging your HXs. So, you will want to provide a monitoring sub-system to continuously check the temperature of the water at the OUTPUT side of your evaporator HX. You'll want the monitoring circuit to be able to shut down the whole heat pump if the temp gets to, maybe 34F or 34F, as a safeguard. Also with your variable speed controller, if it is under computer control, it could do a soft slow down as freezing conditions were approaching. I think it would be best to have two separate systems working to protect your nicely made equipment. Really appreciate your photos, too. It makes it so much more likely that other people who can actually see what you have done, will realize that they can do it too. Great Job!! -AC |
I wish the water tables hadnt dropped here in the area. We used to have (Flowing) artesian wells here. But table dropped the water company drilled there deep well and flows stopped . That would be a great source for a open loop geothermal. No need for a pump
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Hi AC , i have attached a few photos showing 2 temperature controllers , the blue is for evaporator temp and set at 1c to prevent ice up , the red one is condenser flow temp for floor .This is how i will control the temp in the house , with a little test and adjustment to get a comfortable inside temp , hoping to not have to go over 35 to get room temp of 20. That will be the big test.
I also plan to add methanol to the cold loop to give me more protection and prevent any growth or abcteria in the warm season. The stainless steel hx sits in the stream and the company that builds them usually have them inside another stainless pipe that is straight and use them for all sorts of cooling applications. Check out there website vaportec.co.nz It also shows the evap and condenser i used , coil in shell. My next hurdle is securely mounting the stream hx to keep it off the bottom (with testing it was covered in weed and sitting on bottom )but also prevent damage or loss in a flood . Andy http://ecorenovator.org/forum/attach...140304_001-jpg http://ecorenovator.org/forum/attach...140304_002-jpg http://ecorenovator.org/forum/attach...140304_003-jpg |
If it's a closed loop, use a glycol mixture instead of plain water as it is less likely to freeze and will let it be able to run at lower temperatures.
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Mike , yes i will be using antifreeze.
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Any updates on the system geoheatnz?
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Hi there , yes a few things. All numbers Metric .
I have moved the stream heat exchanger to a narrower spot in the stream where it has constantly flow over it , the old place was just the nearest to my shed, this has improved the heat exchange a huge amount. Instead of a 7K water differential i now only get 2K at the same pump flow which has quite an effect on evaporating temp , so happy as with the stream hx. I also have 120m of pipe in the ground from stream to the house which may contribute a little heat to the system. Our weather here at moment does not require heating , just a few 10c mornings. I have run it for a couple of hours each morning for a week just to get a feel for running costs , looks to be about 1 NZ$ an hour for a 3.5kw/hr input. The radiant floor side is running with a 5K water temp so been running the flow temp up to 32c but i really need some cold weather to see how house performs as well. I am using a R22 drop in replacement , R438a . It has very similar characteristics , with lower discharge temp and 5% lower capacity. So just waiting on winter really. http://ecorenovator.org/forum/attach...140309_004-jpg |
Have things been getting cool enough to start using the heat pump yet?
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Hi every one,
well i had a few issues with the stream heat exchanger , performance was excellent but corrision was the problem. i had bolted it to stainless cross braces and where it was touching the tube it rusted out. I am in the process of building new heatpump with bigger plates and poly pipe in the stream . Ill post some pics soon. Cheers Andy |
So can you please elaborate on the original build? From what I can gather, it looks to be an amazing success. A water-to-water heat pump has all kinds of challenges and losses on both sides of the system, so achieving high efficiency (as well as sustained continuous operation) is quite an achievement.
3.5 tons of heating (~40KBTU) for 3500 Watts input power puts it in the range of 4+ on COP. This equates to a heat pump unit that would cost at least $4000 US dollars to purchase, plus probably an equal amount in materials for the indoor and outdoor loops. Being a variable-speed unit, did it perform better at reduced capacity? What kind of pumping strategy (both water and compressor) did you figure out? This topic, as well as capacity control method, is a huge stumbling block for many members. As I'm sure you know, the process is much more complicated than just connecting part A to part B and C and so on until the whole thing just works. Yes, it's disappointing that the underwater heat exchanger didn't last forever, but it looks to me like it could be repaired pretty easily. A new anchoring rig could be devised that would avoid the galvanic corrosion issue. Why are you considering rebuilding the whole system just because the one part sprung a leak? Is the tubing made of some unrepairable exotic alloy, or are there other issues present that make you want to abandon it? I'm certain that other users (besides me) would be very interested in hearing about your adventure making this thing work. The overwhelming majority of people believe it is impossible to make something like your rig work, much less save any money on heating bills. I see pictures that prove it exists, but how could you have done this without a PhD in thermodynamics and an army of skilled tradesmen? |
Hi all,
when i started my original project we had just built the house so budget was tight. I had collected various compressors and pumps controllers etc , i bought the evap and condenser from a local company but their capacity was lacking. There was a 16k approach temp so at 5c water out i was evaporating at -11 , also on condenser the same thing , water out at 35c condensing temp 50c. The compressor was a twin reciprocating piston unit , meant for commercial duty, so very noisy . Given the conditions that the evap and condenser presented to the comp it could not give the capacity needed to get the house warm. Just not enough guts in it!! So pretty disapointed with the whole thing at this point , i really hadnt done my home work on the evap and condenser performance , they where the cheapest option at the point so i went with them. I then discovered the multiple leaks on the stainless stream hx and that was final straw really. I pulled it from stream and into shed and cleaned up and easyflo silver brazed them , i removed cross braces and returned them to stream for rest of winter. The damage was done and pitting continued and i decided i needed to try something different. |
I had a Daikin Ry125luy1 , which is a 12.5kw reverse cycle heatpump , i only had the out door unit and no matching indoor.
I removed all electronics and eev and replaced with a txv . There is a NZ company called Temperzone who build all sorts of a/c heatpumps , they use a simple 230v control board which includes protections for hp , lp , low reffrigerant charge , defrost and delay comp starts . It has 3 temp sensors and also a out door fan speed controller for a/c mode. for I managed to come across two of these second hand and they work great. I had also 2 small plates that i paralled together and used as condenser , these were placed inside my plant room with piping running to the Daikin outdoor. This setup worked well for the start of winter when no defrosts were happening. I only run the heatpump on night rate electric as it is less than half of day rate, i try to get all heating done in this period. When the temps get to 2c or so the unit is defrosting every 30 mins and house is noticeable cold on these mornings. The comp in the daikin is a 5hp scroll , so i know that if i can give it the right conditions it can do the job , so i have pulled comp from the Daikin and am building water to water unit Mk2. |
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Ive attached a few photos , showing condenser with desuperheater mounted above , to allow any liquid to drain down to condenser. Condenser is a dual circuit , ive got a ball valve on one side to increase high pressure if needed.
Reciever will be under condenser and then to subcooler . |
Sorry about photos , ill try to spin them 90.
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It's funny how financial burdens bring out the best in people. Many modern machines were invented by people building something themselves because they could not afford (or have the desire) to purchase a manufactured unit. Such is the road we travel: with experience comes skill and wisdom. It sounds like your unit did better than many others' first attempts.
I have some questions about your current project. Are your evaporator and condenser heat exchangers matched very closely? It looks as if you have a lot more desuperheater + condenser than evaporator surface area. Also, with such a small footprint and such short runs of refrigerant piping, you most likely don't need to worry about subcooling or an additional liquid receiver. That condenser looks like it could hold your entire system charge with ease. |
Hi Jeff,
The condenser is physicaly twice the size of the evap , its a dual circuit plate and i have put a ball valve on one side to experiment with how system performs . These plates are just some items that ive come across but are pretty close to what i need. I have an eev so running a low high side pressure shouldnt be a problem. |
Odd that the stainless stream hx tubes would be corroded by stainless cross braces in a fresh water stream?? Were they radically different types of stainless??
Congratulations on your bending, brazing, tubing attachments etc - makes me ashamed to look at my own! I think you have some experience in this stuff, guy! |
That's what it looks like to me. Most of the commercial units put the oversized heat exchanger on the outdoor side. This has a few positive effects on the system.
First, the outdoor exchanger has less temperature swing on the refrigerant circuit than the indoor exchanger. With a refrigerant-to-water evaporator circuit, this means better superheat control and less oil foaming action inside the HX. The added mass and heat transfer surface area acts to buffer and absorb strange transient events that could cause problems with a smaller HX. On the indoor side, you have a desuperheater coil, so it would absorb a decent portion of the heat. This would reduce the size of condenser HX you would need to take care of the rest of the latent heat transfer. A smaller exchanger indoors helps to get the system producing useful heat faster on every startup. Having too low high side pressure is actually a problem, as higher head pressure (to a certain extent) ensures that your refrigerant condenses faster and at higher heat flow. Especially with refrigerant-to-water, where the refrigerant may need to work extra hard to force a temperature rise in the water. |
Hi Jeff ,
both of these plates are freebies , so im just doing what i can with them. The evap is a 10t or 35kw , so more than 100% over capacity. If i used the dual plate it may be 200% over and i was concerned with gas velocity and oil return to compressor. I think it best to use dual plate as the condenser then i have plenty of room at bottom of plate for subcool and a reservoir for liquid that wont raise the high side pressure. The water is heating the underfloor slab so i do not need high temperature water just a gradual warm up. The closer the high and low side are the greater the COP. Quote Having too low high side pressure is actually a problem, as higher head pressure (to a certain extent) ensures that your refrigerant condenses faster and at higher heat flow. Especially with refrigerant-to-water, where the refrigerant may need to work extra hard to force a temperature rise in the water. Quote If you have the surface area on your condenser the condensing temp will get close to your water out temp , the rate of transfer will slow as the temperatures approach. Its better for the compressor capacity but not for the plate heat transfer , really just economics if you are designing and buying the plates. No good aiming for near infinity. |
No, here's what will happen in your scenario. On a cold start up, the massive condensing action will gobble up your high side pressure. The compressor simply cannot move enough gas to saturate the condenser. Due to the fact that expansion valves are a pressure driven device, the mass flow through the one in your unit will be puny until the condenser builds pressure. Thermostatic or electronic, it doesn't matter. They are designed for a maximum amount of flow at a certain (high) pressure. Below that pressure, they sit wide open, passing however much flow that pressure and/or superheat control will allow.
Heat pumps all do this, and modern units have a built-in (indoor fan) delay to help speed the initial pressure-temperature ramp up. This one small feature is a big time selling point for mini-split manufacturers. With a huge condenser, your unit will do the opposite, slowly ramping up output until useful heat is produced. The effect is not trivial. Every heating cycle, you will be wasting x amount of electrical energy just to get started. My point is this: So what if your compressor is only using 80% energy on startup if it takes ten minutes to build up momentum? Yes, it all depends on cycle time and duty cycle and etc., but a quick start-up will make up for a whole lot of "a couple degrees closer approach". That ultra-super-efficient heat exchanger could keep your desuperheater from working at all. |
These last two posts are superb and I look forward to the dialog between these two experts. By "thanking" both, I am not taking any side, but am very intreagued with the subtle choices that have made this NZ water source heat pump so efficient. But as Jeff asserts, further increases in efficiency are there - so this is a discussion you should follow.
I certainly am learning a lot! Steve |
If the system is correctly charged the unit will begin to produce heat almost immediately , i can understand that a split needs to get up in temp so there is not a cold breeze blowing but this doesnt mean the unit would not condense at a much lower pressure if allowed to , it is just for comfort of the occupantants. The condensing temp is a factor of surface area and fan speed. (if we assume a constant refrigerant flow).
With the underfloor i do not high temperatures so as soon as the system starts , heat is flowing and this will gradually build up as floor warms. Take some ball park fiqures , If at start up my water return temp to my condenser is 28c then my condensing pressure will be 32c to 33c , at this point in time my COP will be the highest as cond temp is lowest and ground loop will be warmest , as the hp runs over the hours COP will drop as conditions change. I admit that it is all theory at the moment , but only using 50% of the condenser plate gives me pretty close to the same size plates for evap to cond. |
Yep, I understand where you're going here. This delves into the theoretical and practical world of mechanical engineering. The main difference here is that in the design phase of most stuff like this, the entire whole thing is modeled on some kind of computer. The engineer(s) then throw curve balls at the unit to try to avoid building a turd. They can do these things easily and quickly because they have expensive simulation programs that rely on formulas and specs that have been reviewed and historically proven in reality. Once the thing satisfies the design team on paper (or on screen), a preliminary build is made and tested rigorously. And then and then and then... many revisions later, the design is finalized.
The main reason for all of the trial and error in the design process is because there always exists a difference between "ideal" and "real". What your theory suggests and what you build for real never equal out completely. If you have very strong faith in theoretical simulations, spreadsheets, and rules of thumb, prepare to be let down when the rubber hits the road. Even with superconducting supercomputers and decades of engineering experience at your disposal, be prepared for Murphy's law and mother nature to wreak havoc on your idea. Happens every day in industry. Back to your project. If I'm being too critical of your plans, let me know and I'll back off. From your past postings, I can tell this project is real (somewhat rare on the internet) and that you have the skill and ambition to make this thing as good as it can be (even less common). As always, you can take or leave any of my suggestions for whatever value you may or may not see. Doesn't hurt my feelings a bit. You said the smaller heat exchanger is rated for more capacity than the compressor you plan on using, yes? With an extra heat exchanger plumbed in series as a desuperheater, your recent post of having 30-35 degree condensing temp doesn't make much sense. Unless your DHW tank is merely "warm", it is going to be sitting there in the 50+ range. If it possibly can, the refrigerant flowing through the desuperheater will rob heat from your hot water tank to feed the floor. If your hot water tank is solar powered, no problem...if it's not, hmm...I can't call it from here. For the sake of reality, let's say your DHW tank is going to top out at 60 degC, and that you plan on maintaining 20 to 25 degC room temperature. If you have a hyper-efficient slab floor with closely spaced piping, you can get away with 30-35 degC return water temperature. This will keep your system from lagging too badly. This puts your supply water temp up into the 40's already. Assuming a 10 degC gradient in the indoor condenser puts you in the 50's on saturation temp and pressure. So topping out in the low to mid 60's on your high-side PT curve may very well happen, even with your oversized condenser and a really efficient slab. On the outdoor side of the system is where you have a hard boundary: the freezing point of water. The fact that you have a flowing stream makes a gargantuan refrigerant heat exchanger very valuable. It will be very difficult for your outdoor heat collector to freeze the flowing water, due to the enormous latent heat involved. If you design it right, the underwater heat exchanger will have a hard lower limit as the thing starts trying to freeze the stream. With a large surface area in the plate heat exchanger, this reduces the refrigerant-to-water delta T, and your hard boundary shows up when it is most needed: the coldest days of the year. What I'm getting at here is it really pays off to maximize your heat gathering ability. The compressor can only move what gas it is fed. A couple of extra degrees on the suction side makes more difference when the unit is running hard. This happens every cycle as well with a hydronic system without some sort of heat store tank. I understand your ideal conditions, but if you want to maximize your savings, what you really need to design for are those really cold days. Then when ideal conditions present themselves, the system will perform better than expected. |
Hi Jeff ,
i have no concerns about discussing design and dont have hurt feelings or anything:) . I fully understand the effects of "over condensing" and have seen the effects on air cooled refrigeration systems several times. Im sure if i could of afforded it , i would of had SWEP plates designed and ordered them , probably costing $1500 -$2000 nz dollars. My house can be heated with a return temp of 30c , going on previous history with the air to water hp . Depending on the out door temp the flow was 5k higher. The condenser then was a 15kw unit and approach was 11c so condensing about 46c . I expect these to be reduced with the new evap and condenser but on the same compressor and same water flow . The refrigerant im using is r407f which has a high discharge temp compared to r22 , the desuperheater pump will only come on when discharge temp over 60c . ok got to go to work. |
Here is a quote on how eevs work from Carel.
Over the last decade electronic expansion valves and controllers have taken a substantial part of the expansion valve market due to the increased energy efficiencies they provide. The EX valve does not rely on a minimum pressure drop across the valve, as a motor drives the valve open and closed. This enables the condensing temperature/pressure to be floated down with the ambient temperature which saves energy. As much as 25% energy savings can be achieved by using an EX valve and floating the condensing temperature/pressure. EX valves require an electronic driver to operate them and are usually available as a kit to make selection simple. Usually a driver kit and an EX valve is all that is required. |
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I assembled all refrigeration side today and have attached photos. Just reversable water side to complete . Only burnt my self once .
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How do you plan to control the electronic expansion valve in this system? I'm satisfied with using TX valves in the units I assemble. I'm sure I am not the only one who is eager to figure out how these things actually perform. The OEM's speak of these devices like they are secret weapons.
Here's an article that is the opposite of what most manufacturer claims are like: http://www.achrnews.com/articles/950...ves-the-basics And the follow up that is intentionally vague: http://www.achrnews.com/articles/942...pansion-valves If you look a little deeper into the design side, the valves are indeed rated just like TX valve as far as selection. They are rated just like the mix and match valve bodies and power heads. What this tells me is that a certain part is designed for the range and refrigerant it will be metering. So yes, you can force a smaller Delta p, but then the capacity of the valve is reduced. Dad blame it, I'm talking like an engineer again! Sorry about that. |
I am using the complete Carel system.
Expansion valve driver E2V fully welded These use a pressure transducer and temp sensor at outlet of evap. |
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