The impact of a building company’s heat distribution network on heat pump choices
Water radiator networks in old buildings are designed to operate at the sizing point for their climate region (depending on the region -26…-38 degrees Celsius below zero), typically at a temperature level (supply/return) of 60/40, 70/50 or even 80/60. The actual temperature level should be measured during the project design phase, as actual temperatures may differ from the design temperatures and the radiator network temperature has a significant impact on the operation and efficiency of the heat pump.
The temperature range of the radiator network can be reduced in several ways: by basic adjustment of the radiator network, by replacing the control devices and by changing the radiators to more efficient models. In addition, the possible reduction in radiator water cooling resulting from the basic adjustment of the radiator network and the resulting possible need to increase the flow rate, as well as the dimension of the trunking (pipe thickness and ratio of pipe thickness to network length) must be taken into account.
Improving structural energy efficiency will also help, including additional insulation in the attic/exterior and replacing windows to reduce radiator water temperatures.
Impact of replacing water radiators on the purchase of a heat pump
You should consider replacing your radiators if they have been in use for more than 40 years, if they do not have sufficient heating capacity or if they are otherwise in poor condition. Old pipes and radiators accumulate scale, which reduces the flow of water and also reduces heating efficiency.
However, it is possible that radiators over 100 years old can still be used if the operating conditions have been good, there is little need to add water to the network and the pipework is in good condition. If acidic “tap water” has to be frequently added to the network, the oxygen-containing water will corrode the radiator network until the oxygen has been completely removed by airing the radiators.
The most common pipe material used in the heat pipe network is steel pipe. Other commonly used pipe materials include copper, plastic and composite pipes. All pipes in the heat pipe network must be oxygen diffusion protected, i.e. they must not allow oxygen to enter the heat pipe water.
Large radiators are efficient at lower temperatures, which improves the efficiency of the whole system. In this case, it is recommended to set the target maximum outlet water temperature of the radiator network at a maximum of around 45-50°C. Replacing the radiators alone is often not a worthwhile savings measure for energy efficiency reasons alone, but when replacing the main heating system with geothermal, air-to-water or exhaust air heat pumps, it makes sense to replace the larger radiators at the same time.
Replacing thermostats and radiator valves improves profitability
Replacing radiator thermostats and radiator valves can be very cost-effective when replacing radiators or as a separate measure. In addition to the thermostat, the radiator control valves need to be replaced, as the performance of the valve affects the performance of the radiator. Even one “too warm” apartment in a block of flats reduces the efficiency of the whole building. The circulation pump should also be replaced at the same time if it has been in use for more than 15 years. Compare the energy labelling of appliances, especially the energy class and the Energy Efficiency Index (EEI), which should be as low as possible.
The service water temperature must be above 55 degrees Celsius
According to the Housing Health Regulation, the temperature of hot tap water from a hot water installation must be at least +55°C and must be obtained from the water heater within 20 seconds. The water from the water heater must not exceed +65°C to avoid causing burns.
- With heat pumps, domestic hot water can be easily and safely heated, if necessary with the help of an electric resistance or other heat generator.
- Some heat pumps have an automatic function that heats domestic hot water to around 65°C at regular intervals, either by means of an electric resistance or by means of a compressor, depending on the model. The tap water temperature must not fall below 55°C, as specified in the Health and Safety at Work Regulation, even if the temperature is raised from time to time.
In building societies, hot water is generally circulated so that each apartment receives hot water within a reasonable time. In older buildings, towel dryers (“rag radiators”) are commonly added to the domestic hot water circuit, as are bathroom radiators or underfloor heating. These can consume so much energy in the DHW cycle that the DHW temperature is not maintained at the required level.
In addition, the regulations do not allow radiators connected to domestic hot water to be turned off or throttled, even in summer, to prevent the reduced flow from causing bacterial growth, which would create unnecessary heat loads in bathrooms during the warm season, reducing comfort and causing unnecessary cooling.
The compliance of the domestic hot water network must be checked when the heating system is renewed to ensure an adequate temperature level. Heat losses in the hot water circuit also have a significant impact on the design and running costs of the heat pump system.