Analysis of Power Quality Problems in Large-Scale Application of Air-Source Heat Pump

With the implementation of electric energy alternatives,the large-scale application of electric energy substitution represented by air-source heat pumps has replaced traditional coal-fired heating,which is beneficial for the environment and alleviates air pollution.However,the large-scale application of airsource heat pumps has brought power quality problems such as voltage sags,harmonic pollution,and three-phase imbalance to the distribution network.This paper studies the fixed-frequency and variablefrequency air-source heat pump,introduces its working principle,analyzes the mechanism of its power quality problem.Moreover,the paper establishes a simulation model for the fixed-frequency heat pump and variable-frequency heat pump to connect to the distribution network.This research mainly studies the impact of large-scale fixed-frequency heat pumps on the depth of voltage sags in the distribution network and the impact of large-scale variable-frequency heat pumps on the harmonic content of the distribution network under different penetration rates and uses measured data to verify the reliability of the simulation results.This paper uses experimental data for the first time to verify the real power quality problems of large-scale heat pumps,which can provide a reference for determining the power quality standards for heat pumps connected to the power grid.At the same time,it can also provide a reference for the power quality management of the distribution network that is actually connected to electric heating.

Novel Radiation-Adjustable Heating Terminal Based on Flat Heat Pipe Combined with Air Source Heat Pump

The electrification of building heating is an effective way to meet the global carbon target. As a clean and sustainable electrified heating technology, air-source heat pumps (ASHPs) are widely used in areas lacking central heating. However, as a major component of space heating, heating terminals might not fit well with ASHP in order to achieve both intermittency and comfort. Therefore, this study proposes a novel radiation-adjustable heating terminal combined with an ASHP to achieve electrification, intermittency, and better thermal comfort. Radiant terminals currently suffer from three major problems: limited maximum heating capacity, inability to freely adapt, and difficulty with combining them with ASHPs. These problems were solved by improving the structural design of the novel terminal (Improvement A–E). Results showed that the maximum heating capacity increased by 23.6% and radiation heat transfer ratio from 10.1% to 30.9% was provided for users with the novel terminal. Further, new flat heat pipe (FHP) design improved stability (compressor oil return), intermittency (refrigerant thermal inertia), and safety (refrigerant leakage risk) by reducing the length of exposed refrigerant pipes. Furthermore, a new phased operation strategy was proposed for the novel terminal, and the adjustability of the terminal was improved. The results can be used as reference information for decarbonizing buildings by electrifying heating terminals.

The noise spectral characteristics and noise reduction schemes of screw air-source heat pump:A case study

The screw air-source heat pump can cause incessant high noise levels during operation,which might hinder adoption of this energy-efficient heat pump.First,acoustic measurements and comparison testing were performed in this research.The measurements revealed that the compressor is the main noise source of the heat pump,and it shows a multipeak frequency distribution and a wide frequency spectrum under different work conditions,with multiple peaks at 63,250,and 1000 Hz.Then,a compressor sound insulation cover with broadband absorption was proposed,and it was experimentally proven that the insulation cover can reduce the maximum sound pressure level of one unit from 89.8 dBA to 79.1 dBA.Third,we proposed several noise reduction strategies and compared their noise reduction effects using computer simulation.The results showed that the noise problem can be effectively improved through the rational design of the sound barrier and the layout and opening options of heat pump.The distance between the sound barrier and heat pump and the sound attenuation due to diffraction ALa exhibit a U-shaped relation.For buildings of different heights,the optimal heights of noise barrier are proposed.The 5.5-meter is the optimal height of the sound barrier for single-story buildings.The conclusions can be applied to other building projects for heat pump noise reduction.

Refrigerant Control Strategies for Residential Air-Conditioning and Heat-Pump System

This paper simulated the optimal refrigerant charge inventory of a refrigeration system in air-conditioning operation and heat-pump operation respectively,and studied the refrigerant control strategies in this system.The void fraction in two-phase fluid region was calculated by Harms model.And based on distributed parameter model and Harms model,the refrigerant charge inventory in condenser and evaporator were calculated and analyzed in air-conditioning conditions and heat-pump conditions,respectively.The calculating results of different refrigerant mass between refrigeration and heating conditions indicate that the optimal refrigerant charge inventory in heat-pump conditions is lower than that in air-conditioning conditions.To avoid the decrease of COP due to the surplus refrigerant in heating conditions,we introduced the liquid reservoir control method and associate capillary control method.Both of them could increase the heating capacity of the air-source heat pump.The difference of optimal refrigerant charge inventory in air-conditioning and heat-pump system can be controlled by the liquid reservoir or the associate capillary.

采用两种常见除湿剂的新型无霜空气源热泵系统模拟研究

针对空气源热泵冬季结霜问题,构建了一款用无机盐溶液作为除湿剂的无霜空气源热泵系统,并应用Aspen plus建立了系统模型,对空气进口温度、进口相对湿度、气液比、溶液质量分数、冷凝温度5个因素构建了正交试验,分别采用氯化锂和溴化锂2种除湿剂进行模拟,将试验数据分别拟合成关于进口参数的经验公式。结果表明:在溶液入口水蒸气分压力一致的情况下,采用2种除湿剂的系统COP基本一致,除湿量变化曲线一致,但采用溴化锂溶液的系统除湿量比氯化锂溶液的高43%～66%,其气液吸热比也比后者高33.3%～54.3%。通过正交试验法分析得出最佳参数组合,并确定了性能因素影响程度的顺序。

板片蒸发冷凝式空气源热泵机组无霜制热的试验与验证

分析目前空气源热泵机组常用的除霜机理,提出热泵无霜运行系统,从原理上消除传统空气源热泵机组室外换热器结霜的必要条件,详细介绍了其工作原理及工作流程,通过试验进行了验证,表明溶液喷淋方式不但能够提高空气源热泵系统的制热效率,还从根本上消除了结霜的条件,确保机组无霜制热运行,提高了机组运行的稳定性和可靠性,扩展了使用的地域范围。

北京地区空气源热泵“无霜除霜”事故的实测研究

传统的＂温度-时间＂除霜控制策略会导致空气源热泵（ASHP）在干燥、寒冷气象条件下,频繁出现周期性＂无霜除霜＂事故。本文针对此问题,在北京市2012～2013年供暖期内,对1台采用传统除霜控制的ASHP机组进行了连续60天的现场测试,从机组的运行和供热特性2个方面揭示了机组的无霜除霜事故特性,统计并量化了测试机组在北京地区应用的无霜除霜事故频次、及其所引起的供热损失。测试结果表明：机组共除霜1 737次,其中无霜除霜1 211次,占除霜总次数的70%。无霜除霜事故集中出现在＂无霜区＂和＂轻霜区＂。无霜区内,机组单次无霜除霜事故所造成的供热量损失和供热效率损失分别为108.3 kJ/kW和5%,轻霜区为156.7 kJ/KW和7%。测试期内,无霜除霜事故所引起的有效供热量损失为139.3MJ/kW。