Solid stone end-terrace, 5 kW Gen 6 Samsung

HeatpumpMonitor.org: System 4.

This system achieved an SPF H4 of 4.4. (3.9 for hot water, 4.6 for space heating).

Key factor that made this performance possible is the design flow temperature of 40°C and weather compensation set to match.

This design temperature was in turn made practical by an accurate heat loss calculation that placed the heat loss for the house at 4.0 kW. The main factors in the more accurate heat loss calculation were blower door test informed air change rates at 0.5 ACH, lower stone wall U-values at 1.5 W/K.m2 (SPAB report), -2 design outside temperature and assuming an occupied neighbor at 18°C. Heat loss increases to 4.3 kW with an unoccupied neighbor.

5x K2 and 3x P+ radiators combined to produce a rated output capacity of 14.7 kW. These radiators provide 4 kW of heat output at 40°C.

A 5 kW Gen 6 Samsung heat pump was selected. This is often considered a budget heat pump, but the results from this system show that it can hold it’s own against more premium brands when attached to a similar system and ran at similar temperatures.

The system is a simple open loop, single zone system. Anti-freeze values were used for freeze protection, the system was flushed well and filled with pure water + inhibitor only (no glycol).

System achieves a fractionally better than average % of ideal Carnot COP or practical efficiency factor at 49.1%.

Key Stats

Property	Value
SPF H4	4.4
Space heating only	4.6
Hot water only	3.9
Proportion hot water	17.5%
Measured heat loss	4.0 kW
Calculated heat loss	4.0 kW
Defrost max output	4.7 kW
Rated output of radiators	14.7 kW
Weighed average flow temperature	33.1°C
Weighted average flow minus outside temperature	25.3°K
Weighted average outside temperature	7.8°C
Weighted average % carnot	49.1%
Design flow temperature	40°C
Design outside temperature	-2°C
Mean flow temp on coldest day	33.9°C
Max flow temp on coldest day	35.4°C
Outside temperature	-1.8°C
Internal temperature coldest day	19.5°C

Default CIBSE comparison

The default CIBSE heat loss for this property would have been ~7.6 kW (A combination of CIBSE category A air change rates, lower design outside temperature and unoccupied neighbors). More often than not this would result in a 10 kW heat pump being installed, 2.5x the actual heat loss.

The system would have likely been designed to a design flow temperature of 50°C, which as is often the case would have resulted in roughly the same size radiators being upgraded/installed (50°C needed to output 7.6 kW rather than 40°C for 4 kW). Had weather comp been set to match the higher design calculation the potential performance benefit of those rads would not have been realised.