I know, low loss headers (LLHs) aren’t necessarily ‘low loss’ but, if set up carefully, those losses may be minimised.
Our own installation ‘features’ an LLH, I didn’t know that they intended to fit one until I saw the pipework and had to enquire what the device was. Once I knew what had been fitted, I was determined that it should be adjusted via the secondary pump to run as efficiently as possible.
The secondary pump (Wilo Pico) has a number of settings including a variable range – and this is the means to run the LLH with as close a balance for the flow as possible. I am using the term low loss header in this article but the same procedure could be used for a 4-port buffer tank as the working principle is the same.
I should say now that the primary pump in our Daikin heat pump seems to run at three different flow rates but the majority of the time, it settles down to the lowest flow rate of ~7 litres per minute; I decided to optimise the secondary flow to match this.
Four temperature probes were attached to flow and return ports (these were purchased from a well known South American river company fairly cheaply as a pack of four and, as such are not calibrated and thus ‘vary’ from each other). It is wise to compare the readings from the four probes and make a note of the differences; please see note at the end of the article about calibration.
The probes are attached tightly to the four ports on the LLH and then covered with several layers of insulating reflective foil ‘wrap’ to give the probes the best chance of sensing the pipe temperatures fairly accurately. I arranged my four sensor displays to mimic the position of the four ports; thus the top left senses flow to LLH, top right senses flow from LLH, lower right senses return from heating to LLH and lower left senses return from LLH to heat pump. The secondary pump (Wilo Pico) is connected to the flow out from the LLH to feed the heating circuit.
With the heating system running and settled down, note the various readings from the four probes – the aim is to minimise any differences between the flow in to the LLH and the flow out from the LLH to the heating circuit. It is also desirable to minimise the differences between the return into the LLH and the flow out that returns the water to the heat pump. There should be a difference in temperature between these two pairs of ports as the return circuit has dissipated heat in the emitters.
The aim is to reduce the ‘distortion’ to the minimum; should the secondary pump be running too fast, this will cause excessive mixing of the return with the flow from the heat pump. It may be a delicate balance to match flow from the heat pump, but if running too slow, less heat will be drawn into the secondary pump from the LLH. This ‘balance’ requires patience and small increments of change in secondary pump speed and then waiting to see the difference such an adjustment has made. After a few iterations, it will become apparent what effect any change is making.
My own setup shows a difference of ~0.1- 0.2C (after applying the correction factor) between in and out port pairs on a good day and when the primary flow is ~7 lpm., this is the best I have managed to achieve. This suggests that I have an efficiency loss of ~0.1-0.5% but I am leaving things at this as removing the LLH and re-plumbing the system is a relatively large step to make in our airing cupboard; the expression ‘leave well alone’ comes to mind!
Calibration of Temperature Probes.
These ‘cheap’ probes are not calibrated and to be at all meaningful, it is advisable to carry out a basic check to discover the difference between the probes before use. Tying all four probes into a bunch and close together, they should be observed over a number of hours and any differences between them noted.
I didn’t place mine in water (though this might improve the reading accuracy) as I was not sure if the probes and leads are sealed and thus water proofed. I did place a Govee device on either side of the bunched probes as a sanity check though. I found that two probes were within 0.2 degrees of each other and the same as the Govee readings, the other two were also within 0.2 degrees of each other but the ‘pairs’ were a full degree apart.
When setting up my displays, I arranged them so I knew that the left hand displays were showing ~1 degree higher than the ones on the right and made the necessary allowance (correction factor) in reading the values. Without spending considerably more for accuracy, I felt this was perhaps an acceptable compromise. Rather than trying to measure an absolute value, this method which shows a comparison, should suffice for the purpose.