siletto

2ACH, isn't that a terrible number? Or is it different than the european ACH50, 50Pa passivhaus measurement method? The goal is 0.5ach there, and as far as our construction goals go, it can be easily achieved with RAL window installs, sealed vapour stop foil barriers etc, not some space tech solutions.

The fundamental approach was like supplying 7°C to the fancoils, and 16-18°C for the underfloor cooling. I get it what you say, omitting the 7°C side deletes the need for buffering. I am not sure if a fancoil gets any meaningful cooling power when fed with 18 water, but I get the idea!

Thanks to all for the replies! The more I ask (and read) the more obvious it is for me that my ideas are not practically doable in a small-scale family home sized building, with a single heatpump. My initial plan was to use UFH for heating and use fancoils for heating at the same time, but the fancoils could be used for cooling(at 7 degs) alone, or combined with UFC(at 18deg). So that every system could be used for heating and cooling, separate or combined. I thought there are come clever hydraulics that solves this maintaining the advantages, but as You say, it cannot be done without normal buffer tanks, right?

There is no problem with heating. The problem is that we don't want to cool the whole house all day, and using only a single fancoil/radiant panel at a time needs way less flow than any heatpump's minimum.

Thanks for the reply! We plan to use the heat pump for both floor heating and cooling with floor and fancoils, so omitting the buffer completely might not be possible, that is why I seek an Optimum method using it. With a friend, on a test setup we came up with a pwm controlled 4 port buffered floor heating solution, but it uses a condensing boiler. It should work with a HP as well, since it is only a pwm circulator, 2 temp sensors and an Arduino, but We've yet to try it. With a pwm secondary pump, One can preserve the buffering possibility in case of any unexpected heating anomaly, but eliminate the diluton of flow temperature. I posted the question to hopefully better understand the possible pump concepts built into the machines.

Hello again! Sorry for posting a new thread, if it is inappropriate here, please move it to the right section. It is a very technical question, and the more engineering-related heating forums still don't answer it. I have a few weeks in the studying or planning of my own heat pump heating-cooling system, and as an engineer, I came across some questions that are basically unanswered throughout the net, or hardy reachable. The question is that how heatpumps control their inbuilt circulators? I'm sure there are many solutions to this, but I seek reply from those that studied/installed more units. AFAIK, most heat pumps use some kind of PWM controlled circulators now, at least the name-brand ones do. Panasonic Aquarea uses fixed "power" percentage, that can be set from the menu, according to the manual. LG ThermaV uses either fixed capacity,fixed flow, or fixed deltaT(5°C), or some "optimal" flow control method, it can be changed from the menu. The cheaper chinese HPs that I came across does not have control change possibility, but they seem to use fixed-ish deltaT. For those models that need external circulators, how would you set it? What if you must use a buffer/LLH, because you have both fancoils, radiators and UFH, or separate wall/ceiling heat-cool and UFH, or multiple heat sources? The best available articles(like John Siegenthaler's) only describes systems, buffer connection schemes at their nominal performance. Even heating design engineers specify components based on max load. If sized well, at maximum capacity the primary flow is usually greater than secondary(given a 5°C dT HP and 5-7°C dT for UFH) the LLH works flawlessly.. But as a heat pump modulates, it usually reduces its pwm pump's speed, so primary flow becomes less(maintaining dT). The secondary pump, which is usually fixed speed, or constant height type, pumps more water than the HP, so flow mixing occurs. The same thing scould occur with antifreeze monobloc heat pumps with plate heat exchanger. It might be sized to have minusculeloss at nominal flowrates. The heat pump reduces flow, but the secondary pump is fixed, so dT on the secondary side should increase(??), because of the still high flow, but lower capacity. Or the forward temperature drops on the secondary side? Or it follows the primary side with a lag? Or it induces "mixing", just as well with a LLH? IN my opinion, the whole anti-buffer hunt is because of this flow modulation problem during part-load. A fixed-deltaT type secondary pump would be the ideal, but only the most expensive Wilo and Grundfos pumps have that feature. If you set a fixed capacity in the heat pump menu, does this means that the Design deltaT(5°C) increases to 15°C when the heat pump modulates to 1/3 capacity? There is only one 2 minute long video about this topic on the HeatGeek YT channel, but no other source talks about this problem, but it would solve all the buffer-related problems nonetheless.

Sure, you can check many manufacturer's website: Uponor Thermatop M Look for Wavin Comfia CD-4, it is not yet released in the UK Rehau chilled ceiling Somehow these radiant cooling systems are not widely introduced to your Country, idk why. As far as I know, it is now widely used across europe, even in our almost-third-world county, compared to the UK or Germany. Interestingly, underfloor cooling is strongly not recommended in Hungary, because you may slip on wet floors if condensation occurs, cool floor is unhealthy to the feet, "warm air rises to the ceiling", etc. Btw, condensation is prevented by using RH metering thermostats. On simple systems, you can set a maximum RH level that shuts down the cooling in the room. With advanced bus-type controllers, you set the buffer tank flow temp to a low temperature ( e.g. 5-7°C), and use a motorized mixing valve to constantly adjust the flow temp to be above the dew point for the highest RH room. It maximizes cooling effect, preventing condensation, while acts as a further "buffer" when it uses up the 5°C water to mix it up to 16-18°C. Yes, it works. It has moderately high costs, but can provide the peculiar cool "church feeling", if done right. To better understand its problems: Combining radiant heating and cooling makes the system not ideal to either tasks. As many of you advised, UFH should be as open as possible, and use the heat pump's inbuilt circulator without any buffers. You basically heat the whole home, every room. This radiant cooling system always use some kind of room thermostat, and unless you have every ceiling full with these panels working all the time, you don't necessarily have the necessary flow rates to prevent short cycling. I planned to install these panels only in the Bedrooms, but it results in less than 9l/min flow all bedrooms engaged. A single room uses about 2-3l/min, so you either cool the whole house, or nothing. We are starting to be a Mediterranean country in terms of summer weather, but still, cooling is not used for more than 2 weeks at a time, and it can be switched off at night. Why am I bothering with all these unnecessary hassles? Because a very good, silent fancoil(Like the Innova Airleaf that Panasonic sells rebranded to their Aquarea lineup) costs more than these radiant panels for a given square meters of room. The fancoil costs as much as the panels, but you must buy overpriced modulating thermostats, specific comm. boards, drain pans, etc. Still, the small flow problem persists if you plan to cool 1-2 rooms at a time, and a buffer is needed. If anyone has any engineering data regarding radiant floor cooling, I could awfully thank if he/she could share with me.

But the cooling does not only take place in the UF slab, but also in the suspended ceiling radiant panels, which needs approximately the same flow as a slab UFH, but has zero mass. (Uponor Thermatop system)

I downloaded the LoopCAD trial version, modeled the house, so I got very useful results, I really suggest everyone doing this, it is really straightforward, albeit i studied building physics for a year. Basically the program suggested 100mm CTC piping for rooms with many outside walls, and 150mm CTC for rooms with few outside walls. Even using this variable floor piping, there is about 30% difference in flow quantities accordig to the program, that is why I asked if this "all open" method works. How would you combine it with zoned cooling (perhaps only one room at a time with ~0.15m3/h flow)? The manufacturer of the slab/drwall radiant cooling panel suggested a separate cooling buffer tank. The radiant panel needs about 18°C water, so filling the buffer with 5-7°C flow, then up-mixing it may provide the buffering solution. At least it is their idea.

You should have very good insulation! My house is perfectly good with the latest insulation and lifetime emission regulations, although not a certified Passive House. The heat loss per calculations greatly depend on the filtration number between 5.5-7.5kW. If you open all flowmeters, and you don't use zoning, how do you balance the system for "equal" room temperatures? The "standard" UFH layout per my studies uses a Constant Head circulator, but according to your suggestion it is not needed without zoning, right?

Thanks for the reply John! In our climate, almost every installer use some kind of buffering technology. It's because we have to size the HP to a greater span of heat loss. It needs to be sized for winter loads(-15°C sometimes), so heating without cycling is almost nonexistent. In my example: I need about 8-9kWatts of heating at 35°C flow temp for the winter. A 9kW unit might be a good choice, but even a good quality unit can only modulate down to say, ~4kW which might be exactly the load you size the machines there at the UK -2°C. Above freezing(about 5kW for me) the heat pump will eventually cycle. With this "oversized" approach, a second problem comes. If I set the WC curve to supply 30°C water in 0 ambient, The 5kW power with 5 deg deltaT results in so little flow that with your "all open" approach, the secondary(UFH) flowrate surpasses the heat pump's builtin pump, thus severe mixing occurs. Mixing can be avoided only if you fix the flowrate at a constant maximum, but it increases deltaT in low-load conditons. I've been learning about sizing hydronic equipment for quite a few weeks, and I am more and more convinced that part-load calculations are basically nonexistent. Everyone talks about inverter-driven heat pumps, but no one about the fixed speed secondary circuits.

What do you think, how much energy is lost in the 4-way tank reversing valves? I mean the flow and return essentially contacts the same brass body, heating/cooling each other. I am still confused with the 3-port vs 2-port configurations, many articles describe that the 3-port method is the neater, because at least the lower portion of the tank is engaged at all times.

Thanks for the reply! By 'Managing buffer temperature' you mean the start/stop of the HP? Do you think the 2 port is better instead of the 3-port?

Yes, almost all new homes, apart from the very basic, low-cost ones use these panels. It is either a metal sheet with small heating pipes embedded, with drywall overlays or drywall boards with pipes embedded from the factory. It is fixed to the ceiling, or cast in the concrete ceiling. They work very well, but only with ventilation and dehumidification included.

Here we size the heating system to -15°C, so the heat loss of the building is around 8.5kw net, maybe 9kW with losses in the distribution system. Frankly, a modulating condensing boiler is a way better approach in our climatic area, because in winter it is often foggy and around 0°C. ASHPs are way better in UK and warmer climates. Many heatpumps struggle with defrosts and keeping the performance at low ambients, that is why we need to size a 10-12kW ASHP that can still provide 9kW at -15. Due to EU regulations, condensing boilers cannot be installed in new homes alone, only along with 3-4 minisplits or PV panels(with very low return of investment). Buying a heat pump only for heating, and installing air conditioners for cooling seems to be a waste of money. There isn't enough space for floorstanding ultra-quiet fancoils, but the looks and noise of the high-wall, minisplit-like fancoils are very disappointing. The radiant panel ceiling heating and cooling becomes more and more common here. It has very good thermal comfort without any noise. Its only weakness is the humidity factor, because we use 15-18°C flow temps to cool, either with humidity sensors, or condensations switches. Btw a fancoil "indoor" unit costs alone as much as a complete minisplit set, with more noise, less eficiency and more pipework.