Heat Pumps at Higher Roylands: May 2011

Thursday, 5 May 2011

A van load of insulation

Just in case you ever wondered what a van load of insulation looked like.

Having spent all the previous night obsessing about the VRB141, I spent last night on the VRG141, since that is what I have and the distributor wants to use it. The key is what the Sanyo controller does to the ARA672 actuator.

In the neutral, or central position, the valve paddle is straight up and down, connecting the bottom port of the valve to the top port. The Sanyo controller, working with the actuator, expects a 45 degree clockwise rotation to connect the coldest feed to the top port of the valve, and it expects a 45 degree anticlockwise rotation to connect the hottest feed to the top port.

To achieve that with the VRB141 unit, the hottest feed enters on the left hand side of the valve and the coldest on the right. For the VRG141 unit, the hottest feed enters on the right and the coldest on the left. If you get that wrong, you're system will never work. If you're heating installer is unaware of that, there's a 50-50 chance it will work!

Figuring that out was one way to spend an evening. I can think of others.

Wednesday, 4 May 2011

More on Valves

Curioser and curioser. Lots of calls today about valves, including with Martin Hook from Southwest heat pumps who's the franchise holder and knows these units inside out.

Turns out the VRG141 unit is the one the designer intended. Although the Sanyo datasheet specifies the VRB141, and the valve manufacturer's application note shows the VRB141 in that application, Martin prefers the VRG141 unit in this application. Part of it is because we aren't using the Sanyo tank, but a home brewed one that gives us a higher Coefficient of Performance (COP), and part of it is because of the way the valve works.

This being Devon, I wonder if the fact it's cheaper too has anything to do with it?

Tuesday, 3 May 2011

Not all valves are born equal

One diagram shows the operation of the VRG141 valve and the other the operation of the VRB141 valve. Now, think about phoning this through to someone - easy for them to hear G as B or vice versa, or if you're just a tiny bit dyslexic, or rushing, its easily missed. Looking at the diagrams, they are much the same - four holes in the valve, and a paddle in the middle.

But the difference between the two was enough to stop my heating system from ever working correctly. I spotted it by chance - nosing around to find ot what the valve actually did, and I just happened to notice a subtle difference in the letters between what the installation manual called for, and the user manual and the empty box that I was looking at.

The one I want is the VRB141, and it's the lower picture, but the one I've got is the VRG141....

When pipework attacks!

The first "fully commissioned" tests ran overnight on Monday 2nd May 2010. Something felt odd - the radiator feed pipe was always at 65c, even though the heating system had reached its goal temperature, and all the TRVs in the house had shut off due to being at the right temperature. There was also convective circulation in the heating system, which felt like the wrong thing to have.

It took about 16 hours of pondering and checking to "get it." The radator return pipe and feed from the cold part of the tank were swapped around, meaning the four port valve was always delivering hot water, even when it thought it wasnt. The controller was getting confused, and hot return water from the heating was being delivered to the wrong part of the tank.

The plumber came round on the evening of 3rd May, and it took a couple of minutes to explain the error to him. Then a couple of minutes more to convince the distributor's representative as well.

Paul's back on Friday 6th to partially drain down the system, re-fettle the pipework, and add the inhibitor and other odd tasks. Hopefully we should be good to go.

System Schematic

Click for larger image

Bad Things 1 - Single Channel Control Boxes

Count the number of control boxes carefully. You should see there are two. You'll also see a box containing a relay and what looks suspiciously like a "normal" two channel timer switch.

The two control boxes are needed because the control system from Sanyo doesn't accept that you might need two or more heat pumps from one controller. There's plenty of room in the box for an extra signalling cable per heat pump.

But since it's not good enough to do that, all the heat sensors (except for the room stat) have to be duplicated. You have to program them to accept the same temperatures and times of day in order that they may work roughly the same. Silly.

The extra time switch is because the controllers want the heating circulation pump to run pretty much 24x7. The only time they'd stop is when the temperature is above the "summer limit" of (a programmable) 16c. The time switch is an optimisation from the distributor to overrule that. The jury is out on whether that works effectively or not.

Good Things 1 - The heat exchanger

This puppy is my favourite bit of the whole system: the domestic hot water heat exchanger. The blue tank holds water at 65c. When you turn on the hot tap, a flow valve notices the fact, and turns on a pump. The pump circulates water from the blue tank round the "hot" side of the heat exchanger.

The water in the tap flows through the cold side of it, and reaches the same temperature as the water circulating in the hot side.

The net effect is near instantaneous hot 65c water at 26 litres/minute. When mixed with cold water at the bath tap, this fills a bath in about 5 minutes. There's enough capacity in the thermal store to transfer heat to two full baths of water before it needs a bit of a top up from the heat pumps.

The two white things on the left side are the heat-exchanger pre-heat system temperature sensors that me and Paul came up with. They will be fitted to the heat exchanger.