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Robur Heat Pump News...

Not that this means much to most of you but Robur has just authorized a change in the lower limit on the ODT operating range for their new gas fired absorption air source to water heat pumps (GAHP-AR). Originally the units would automatically shut down below -4*F ODT. They have been reauthorized to now operate down to -20*F ODT before shutting down. The change only requires a simple parameter change in their control board settings.


  • Weezbo
    Weezbo Member Posts: 6,232
    That sounds like a step in the right direction...

    thanks for this up date. to day cable computer owners here got cable t.v. for "free" :) i like hearing good things from time to time.

    i was wondering how those two that you spun in made out this last winter.

  • They have done very well. Function has been flawless. We DID lose a condenser fan motor but that was due to construction site dust getting into the bearings. Last I heard for the month of January while under construction we heated ~9000 sq ft of living space plus basement and garage slabs for $347 in gas and probably less than $100 in electricity. His whole electric bill was $150 but some of that was power tools. We'll have more accurate and most likely better numbers next heating season once they've settled in. Meanwhile, my sheetmetal contractor friend with the low end Viessman and hydro air paid $2500 to heat approximately half that area the same month, again under construction. So I'm pretty impressed. Unfortunately the sticker shock on them makes it a little tougher to make the sale and they're only making 5 ton units right now which takes the smaller projects out of the picture. I've been on them to develop a three ton. I know I lost at least two possible sales because the 5 tonners were just too big / expensive for the applications. Both went Geo instead. My friend is seriously considering trading his Viessman for a heat pump. ;)

  • Of course it never did get below -4* here but I shut them down a few times and let the system circulate unheated. It settled out at 86* water temp and held there for the couple hours they were down. THAT was promising!
  • Troy_3
    Troy_3 Member Posts: 479

    What am i missing here? The last robur serval i installed used a basic outdoor boiler setup for the gas heat side. They claimed around 80% eff. Not bad but not equal to condensing. Have they changed something?

  • Oh yea! I posted here on it a while back but came off like a salesman I guess. Oops...

    Robur has taken the old Servel type unit and developed a reversible gas fired absorption HEAT PUMP out of it. The best way to describe it is their method takes heat from the gas fired ammonia circuit and combines it with heat extracted from the outdoor air and heats the glycol solution with it. There is NO conventional gas boiler on these. They claim an average of 126% efficiency (100,000 btu in / 126,000 btu out) but on mild days the actual performance can exceed that. At one point I saw a performance chart at their website that claimed as much as 157% on a 65* day but unfortunately I don't seem to be able to find that particular chart anymore. It also claimed that with 120* water out it will run at 100% efficiency at -4*. I have no idea where the chart went though.

    Originally, AFTER I installed them, they informed me, "Oh, they shut DOWN below -4* ODT." and almost caused me to go into a seizure. Just yesterday I got the news that I can lower that parameter to -20* ODT.

    I'm using them to heat/cool a house I did partially with radiant floor warming and combined with hydro air. I originally wanted to use the conventional Robur/Servel because I wanted to do the house chilled water for A/C (6 zones)and stumbled across the heat pumps during the research process. I've installed the very first two in the whole Western Hemisphere. Mine have been in about a year. They have been in use in Europe for about 3 years now.

    Here's the best part. I'm only running 110* water for heat. (I may increase that slightly) Because you size the heat/cool coils for cool they are WAY big for heat so with only 110* water to them and the fans running on low speed the air actually feels WARM coming out of the supply registers. Show me another heat pump of ANY kind that will do THAT! :)

    Even though I didn't need it for my application they will push up to 140* water out but naturally, efficiency will drop.
  • Weezbo
    Weezbo Member Posts: 6,232
    Well, *~/:)

    here i am again to ask just how well they worked last winter and if they managed to keep up during any cold dives last winter..

    currently we are experiencing some very different times...

    solutions are being diligently sought after by many people in a quandary as to how they will be able to meet the skyrocketing cost in our area for home heating.

    Went to a "Pep rally" mayors conference yesterday evening in our community..it was slightly disappointing in its approach to the conversation with our legislatures members who bothered to show up...

    this is the United States of America and yet one would wonder how we have yet to have as a people any 'United" representation with the very government we elect...

    sorry, i digress....
    thing is our countryside peoples are scattered about in very small towns and villages..they need relief and representation...luckily the Man upstairs is watching over the struggles of the peoples... these heat pumps clearly seem to have some decent ability to dial down the costs of home heating...there might have to be some modifications made to get them to function here and they may be somewhat limited in certain parts of the year..

    however they have my interest ...if you have a dull moment, would you check what the energy consumption was like on them last season ? it might pay for itself in one set of shoulder seasons here ... deep winter the people may have to bite the bullet and fire up the oil guzzler..


  • Funny you should ask... ;)

    I was just there and after I did some mid winter tweaking of the DDC settings (a few months back) they claimed they spent as little as $250 a month for NG the last couple months of winter to heat ~12,000 sq ft. I am still waiting to see the bills but things sound very promising. Keep in mind though, this house is very well insulated which certainly contributes to the exceptional numbers. Here in CT the Dept of Public Utilities has authorized as much as a $75,000 rebate per structure for upgrading to the heat pumps. They have also sold a few more here. I believe there are a total of 8 now installed and running in CT. Check the June 23rd issue of "The News" for the interview they did with me, I gave away a few of my "secrets". ;)

    I'll post more as it becomes available, I'm headed there again next week and may get copies of the bills.

    The only mod I see necessary is if you expect the ODT to go below -20*F you'll need some supplementary heat as these units WILL shut down below -20. Probably a mod con would be best is what I've been thinking. The other thing is glycol concentration. It must be heavy enough to allow FLOW (Not freezepoint) to at LEAST -10*F. On my project I used glycol throughout the entire system. Next time I plan to use a flat plate exchanger so the only glycol needed is for the heat pump circuit and then I'll use water throughout the rest of the structure. I'm not a big glycol fan.
  • Weezbo
    Weezbo Member Posts: 6,232
    Thank you for keeping all over it for the last couple years..

    i would like to ask you if the shut down is more of a runtime function than an OAT per se....

    reason that i ask is , if the off cycle is more dependent upon run time there may be some work around that i could come up with..
    as it is a fuel burner my other question runs to maintenance and any observable minor technicalities that you may have noticed during winter..
  • Not sure,

    exactly what you mean. The unit(s) do have an outdoor air sensor that can be used to control the function as far as switching from off/heat/cool automatically. I find it to be sensitive to the influences of direct sunlight on the outer surface of the area where it is located. I also found cases during spring and fall when it would run cool during the day and heat at night due to the wide temp differences that can occur at those times of the year. This seemed to be defeating the conservation idea so I now switch them manually per the season. I JUST showed the customers how to do that for themselves (again) as a matter of fact. The system as a whole was a bit complicated for them at first but they're getting the hang of it. ;)

    Now, as far as actual run time during operation, THAT is controlled by the water temp settings. You can set them up to monitor incoming or outgoing temp and they will fire up the burner when the setpoint is exceeded by an adjustable number of degrees. This is where I have had the most difficulty. They treat setpoint and differential a little differently than what we're used to. Example: I have two HPs hooked to my DDC. When I set my "setpoint" that is the temp at which the burner will de-energize. The differential will determine when it will re-energize. With one HP it is very straightforward, if I set my warm water setpoint for 110* and my diff for 10* the unit will deenergize the burner whe the water temp reaches 110* and reenergize when it drops to 100*. Once you add more HPs it gets a little tricky because now the DDC will divide the differential according to the number of HPs it controls. So If I have two then at setpoint 110* the unit will deenergize the burner. As the temp begins to drop the ddc will now reenergize the burner in one HP at 105* and then if it can't keep up it will call in the second HP at 100*. As the water temp rises it will then deenergize HP2 at 105* and HP1 at 110* Get it? Add to this the fact that once the HP setpoint is reached the burner does shut off but the HP will continue in what is called it's "spin down cycle" which is 10 minutes and actually continues to provided warmed water to the system during thast time. It can cause the system water temp to actually EXCEED the setpoint after shutdown if there is not much of a load on it. Then on the opposite end, if a HP is completely shut down, no burner, no pumps, it has a "spin UP" cycle that is 7 minutes long. So upon call it takes 7 minutes before the burner comes on and it actually starts producing heat. If you put this all together and set your differential too tight what you will get is a situation where upon a call for heat you first HP will go into spin up, if, during that time, the water temp drops below differential setpoint the SECOND HP will go into spin up before the first ever fires the burner. Consequently at some point you'll have 2 HPs going when the load really only requires one. Then, on shutdown, the opposite will occur. Both HPs burners will have been shut down but will both continue into spin down, keep providing heat to the system and together they will exceed setpoint before they both shut down completely. The they'll do it all over again. The trick is to set the diff so that water temp can have time to react before the DDC wants to call in the second HP. I found 16* on cool works and the midwinter tweak I made was to take the heat diff from 5* to 10*. Once the HPs were working in a correctly staged manner the gas and electric bills went way down and customer satisfaction went way up.

    After all that I'm not sure I answered your question, fire away if I didn't. I'll post a bit on maintenance later today, gotta go right now.

  • A little more,,,

    So if the diff setpoint is not exceeded by the end of the 10 minute "spindown" cycle the unit will shut down completely and will remain that way (as far as I can tell) until the water sensor(s) detect that the static water sitting in that area has exceeded diff setpoint, at which time it will go into it's 7 minute "spinup" cycle which starts the refrigerant circuit pump and the water circuit pump. If, after 7 minutes, setpoint remains unsatisfied it will fire the burner. Then, when setpoint is satisfied, the burner will shut off and back into spindown we go. IF diff setpoint is then exceeded again during spindown it will cancel the spindown, initiate 7 minute spinup and then initiate burner again after spinup. So, under most load conditions, what we end up with two units is one unit which is always in either a spinup or spindown cycle and initiates burner intermittently while the other one remains idle. It can have as much as 17 minutes of spindown + spinup cycle between energizing the burner. I like to call it "feathering" the fuel in and out, kind of like you do when your car is coasting and every once in a while you give it a little gas to keep it going. While the GV itself does not "modulate" the overall effect is the same. You never put in more than exactly what the load calls for in fuel. And again, in both spinup and spindown it continues to heat or cool but at a diminished rate. I have seen the units go into spinup from a dead start and before fuel is ever introduced they are giving 10* delta T across the exchanger. On light load days it is entirely possible to satisfy the system without ever employing fuel.

    There ARE several ways of controlling the operation. Single units have simple r-y / r-w terminals that are compatible with t'stats but if you go DDC for multiple units it can be controlled internally OR externally as the application requires. You can also control the system by ambient space temp sensor put through the DDC as well.

    The DDC does control average run time between the units. I find that even now after two years they are within 10 hours of each other as far as run time.
  • Maintenance...

    There is a cogged belt and pulleys, they recommend replacing the belt and one of the pulleys (can't recall which one) every 3 years. Fairly simple. They also recommend dismantling and checking/cleaning the generator (combustion area) every 3 years as well, a bit more tedious and complicated, once you've done it it goes faster the next time. There is an oil level in the refrigerant side pump that must be maintained, correct glycol chemistry must be maintained and the condenser coil could use regular washing in some areas. They recommend NO coil cleaning solution, just plain water. Solution might strip the black coating off the fins and reduce the heating efficiency. The black coils WILL absorb lots of energy from the sun if they are placed in such a manner that the sun can reach them. A trick I heard about is to plant trees/bushes around them that will shade them in summer and allow sunlight through in winter. I thought that was a pretty slick idea. ;)

    Other than that there is not much to do. I'd suggest a quick checkup before each season on the coil, oil and glycol and then the beginning of every third winter you do the belt, pulley and generator.
  • Correction...

    If you expect the temp WILL go low enough to cause them to shut down, you'll need to protect flow down to maybe -30? They do have "anti freeze protection" which I believe consists of turning on the water side pump to maintain circulation. The thought is, however, that the function COULD fail for one reason or another so it's still wise to protect to the proper temp for your area.
This discussion has been closed.