Altherma flow temp issue

[MikeHolm]

I thought it was only parts of North America that dictated double wall HX for DHW. It depends, of course, on what is on the other side of the HX. Municipalities have always been paranoid about litigation so some demand it when non toxic glycol is used, a hold back from when ethylene glycol was used which almost never is used now. It is relevant here because, in solar, using a double wall makes the financial effectivness of the system questionable due to lowered performance. It must have issues with HPs as well.

[yinmorrison]

Thanks Guys I thought as much. I will have to give the matter more thought.

[Jon Glanfield]

So what we need to do for ASHP's, that generally in the UK, are simple external units is identify a good supplier who can confirm coil size with a 5 degree delta t to match the size of the buffer and the flow temp we intend to spec?

I have mailed Webram so hopefully soon I will be able to receive PM's because I would be interested in hearing which suppliers you use BF.

Just to be clear too, the 100 litre buffers that we have used with the IVT pumps are not IVT designs, they are from well known Heat Pump company based in the UK with a wealth of experience, whether they are just passing these sizings on from IVT though I don't know. In fairness we have not experienced any dissatisfied customers but the units may not be operating at an optimal level.

BF how do you deal with a situation where space simply precludes the use of a buffer on an ASHP project, do you just elect not to take it on for reputational reasons? Also do you find that it makes you non-competitive if an alternate quote excludes a buffer which could also confuse customers who may already be a bit baffled given the new nature of the technology?

Out of interest too, have you arrived at the 30 litres per kw from trial and error, empirical means or manufacturer advice?

Cheers

Jon

[Bigfreeze]

Jon,

Ideally that is what you should be looking for from the buffer. Once you find equipment that works correctly, settle on it and do as little deviating from it as possible.

In a situation where a buffer is simply not an option, we will only install where we can go straight to screed on weather compensation. That way you are guarantee the flow rate through the machine on heating. On defrost, on the machines we work on we have an option to energise another valve/pump once the water temp gets below a certain temp. We usually set it up that once the water temp drops below 20 on defrost, the two way valve on the dhw tank opens in order to increase flow and increase energy available to complete the defrost.

We turn down about 20 installations a year on the basis that they are not suitable for HP applications i.e on standard rads, poor insulation levels in houses etc. It doesn't really matter that they may run for slightly cheaper than oil. The fact is that, these customers will expect dramatic drops in bills and when that does not materialise, your company and your products will be blamed as being shoddy (no matter how well you explain that it won't be the case) . We work on the basis of installing HP's in HP orientated houses i.e good insulation, ufh where we can guarantee running costs 1/4 to 1/5 the cost of oil. It took a while to build up the reputation but the return custom when you work like that gets better year on year and heavy investment in advertising etc is not required.

I don't really care about being uncompetitive. If it means compromising the efficiency of an installation by cutting corners to match others I'll walk away. I've found down through the years that the customers who don't heed advice and don't really see the benefits of why you're doing what you doing, are generally not worth having. Its the guys who are really interested in what you're installing and why that give you the least hassle after sales. People who chase the bottom line I have no time for. If you're buying a Hilti or a Ryobi, you understand why you're paying the money for the Hilti. It should be the same with heat pumps.

The 30L kw was a manufacturers recommendation. But also I've seen the benefits of it down through the years. We do alot of troubleshooting on poor installations and its then you really see why you should install heat pumps in a vey specific way.

[MikeHolm]

[When designing a buffer into a system, which is better a 4 tapping unit which would require pumps up and downstream, or a 2 tapping version which T's into the space heating flow and return, and only starts to heat when static pressure increases as zones close and forces water into the vessel? This could mean a reduced number of pumps and hence power consumption and less heating of the thermal mass until zones satisfy. ]

I'm a bit confused. In an above post it was mentioned that pumps for the UFH be both up and downstream.... on both feed and return????, if I read that right it means that each zone needs 2 pumps. I see no purpose for this.

If I am wrong please tell me what the above means.

Thanks

[Bigfreeze]

Mike, you put your pump on your return to the heat pump (pumping through the resistance) and the pumps on your ufh would be on your flows (again pumping through the biggest resistance), either just one pump or one pump per manifold depending on set up. The HP would be considered a seperate circuit. Which post had the configuration you mentioned in it, as, as you say, it serves no purpose.

What Jon was proposing there was that the buffer be used almost like a receiver, where excess flow could be diverted until the loops in the system reopened. It would work, but again would compomise efficiency

[Jon Glanfield]

BF, we contacted various manufacturers today interestingly and we got responses ranging from 10l per KW from IVT to 30l per KW from Stiebel Eltron with 20l per KW from Nibe.

I think we will be aiming for the 30l per KW though that you have suggested, I have also approached Mitsubishi for their views on buffer usage generally and will be doing the same with Daikin, although they do always say LLH's but we'll see.

Mike are you thinking of the standard Ecodan set up which has a pump on the flow from the HP and a pump on the return to it to increase flow rates by pushing and pulling around the system. These are before any 2-ports and a flow setter on the return to provide a read out of the flow with a retarder in case it is too high, which it never is!

These set ups generally do not incorporate any buffers due to manuf's instructions recommending against their inclusion due to the inverter and so on. Recently though they have changed their literature to mention the potential need for a LLH on UFH to overcome high static pressures and anecdotally today we heard of another big Ecodan supplier using buffers on twin Ecodan installations.

Cheers

Jon

[MikeHolm]

Being from Canada, we don't have any Ecodans yet. Actually, none of the Japanese makers sell an air to water HP yet and are only looking at it now. Also, I think all the air to air ones sold here are 407 or 410, no CO2 either. I am not referring to anything I have experienced here at all. The way the post was written it seemed there would be one pump on the feed and one on return of a zone and that is dumb. One going to the HP and one to each zone is understandable.

[mad fridgie]

In NZ we do also use 2 pumps (push/pull) but this is for economic reasons. There is not a great use for inline pumps, so in many cases it is a lot cheaper to install 2 pumps in series (if pressure is required) or 2 in parrallel (greater flow), than using one correct sized pump (selections made using pump curves).
The buffer tank, I do not think you should use a blanket rule for all applications, but you do need to understand your system.
1: no controlled UFH (fixed water flow rate) i do not see the requirement either a buffer or LLH. (assumed flow rate is suitable for all aspects of the system) The floor is the buffer
2; partial control of the UFH (limted control of some zones, where the flow rate passing through the underfloor never drops below 50% of design, not to be confussed with by-pass valves) The floor becomes the thermal buffer. I would install a LLH Dedicated water pump for HP loop
3; Totally control of UFH and rad systems, where heating loop flow could drop to close to zero, I would install a buffer tank. dedicated pump to HP loop.

Re the size of the buffer tank, if we accept that its primary use is to complete defrosting, then the size should be based upon the flost loading of the evap. (face area * coil depth) this would give the max amount of ice formation.
You then calculate the energy required to melt/remove the ice. Then use this figure to determine the tank size,
You have choose want temperatures you use. It would be a fair assumbtion that the water enetering the cond (evap when in defrost) should not be below 10C to ensure the heat exchanger does not freeze, you should also assume that the house is not up to temperature, and that the water being circulated is also not up to temperature, this being the case the water may only be around 20C. So size you buffer based upon a 10C drop during defrost. (very conservative sizing method)

[MikeHolm]

Mad, I would like to know what type of pumps you use in the push pull arrangement. I am going to do this all from memory so forgive me if some of the numbers are wrong but If you need 40L/m, for example, through a typical large BPHX a Grundfos UP 26-99 should suffice. It may even be a bit big. Its wattage if memory serves is about 250w and should be good for 7m head. Given the above condition would you use two UPS-15-58 pumps with one on either side of the HX? Where does the economy happen when there are twice as many pump flanges and electrical hook ups (I know that the wattage on a 15-58 is less than 100w)? Is it mainly the reduction in wattage?

In many cases where pumps are placed in series one pump will fail before the other as the load on each pump is not exactly the same, which of course, will cause the rest of the system to eventually fail and i would expect the stress on each pump to be different depending on which one is pulling (closer to cavitation on the curve) or pushing. ( I have seen the failures with series pumps many times in drainback solar systems where a high lift is needed to overcome the air in the system until flow is established) Heat pumps are under less thermal stress than solar so I may exaggerate that a bit in this case.

BTW, Unless forced I don't use anything other than wet rotor circs either.

[mad fridgie]

Hi Mike, Grundfos great pumps, hardly never use them, a small fortune here for inline pumps (very limited market)
Tend to use Wilo, OK, better than most but not as good as Grundfos.
We purchase the pumps with the fittings (so no extra costs) a 100 watt pump (25/6 i could be wrong,) from memory costs about $130 (US$100) and thats a lot compared to what i see in the UK, but I if i require a 250Watt pump (more flow and slight more pressure) i pay approx $600 (US$480), thats a big difference in our neck of the woods. Wiring is about 10mins, so about $10. It is a closed loop so i do not have any techincal issues, if one fails then system fails OK i can live with that, as if i only installed one pump and it failed then the system would fail.
I do not worry about cavitation to much on my systems, 1.5 bar standing head and only really working at temps no more than 40C and hopefully no air?????. (Higher for DHW but do not use this method)

[MikeHolm]

That's understandable. Wilo only came to North america a few years ago and matched cost with Grundfos, less 5-10%. The cost for a Wilostar as you noted above is about the same as you pay but the Grundfos is close to that as well. I assume you speak of cast pump and not bronze. The 250w pump will be $250 so for us, I cannot see the issue.

The one bug bear I have is that with a couple of exceptions, we must buy a 2 bolt flange on all pumps. They are bulky and the bolts are difficult to remove at times. Unions are generally not available here except on SS pumps.

[MikeHolm]

Given the cost of pumps in Europe, I still cannot see the reason for a push/pull arrangement on either side of the HP HX unless....a pump is not available with the flow rates needed and I cannot believe that would happen.

[Bigfreeze]

Wilo are about 60% the cost of Grundfos here Mike and for my money they're more reliable. I've had alot of Grundfos units split around the head. Never have any problem with Wilo. We use Lowara on larger pumps. Find them very good aswell. We would also use pump unions and shut off valves rather than pump flanges (screw on type) as the isolators fail to easily and they restrict flow more. We would usually get away with a 25/6 up to 12kw because of pipe sizing etc. That pump is only about €40

[MikeHolm]

I haven't got a pic of our pump flanges to send to you but if you use google.com and look for grundfos in the usa you will see the flanges. They are nothing like ones you mentioned and are far less versatile in some ways than yours. I am jealous of your pump prices and Mad should be even more jealous.

[Bigfreeze]

I know the ones, horrible things. We only really move to flanges on 40mm pumps. Grundfos are ridiculosly expensive here. A 25/80 could set you back €300 plus

[MikeHolm]

BF, would you be using two of those 26/6 pumps in a push pull arrangement on a 12kw machine?

[Bigfreeze]

No just the one Mike. We usually come off the machine in 1 1/4" pipe and manifold out to inch depending on the number of runs. Ufh circuits are usually no more than 80m in length so the resistance in the system is kept low and we can use a small pump in order to keep 5k across the coil. Most 12kw installs I see are using 25/80's but thats just bad pipework design that requires that as far as I see